Toolkit window stays empty if current cluster isn't reachable

[adietish]

Steps:

1. ASSERT: have an unreachable current cluster in current context (ex. stopped minikube)
2. EXEC: launch plugin

Result:
The toolkit window stays empty, nothing is shown. Also there's a fatal IDE error:

io.fabric8.kubernetes.client.KubernetesClientException: An error has occurred.
	at io.fabric8.kubernetes.client.KubernetesClientException.launderThrowable(KubernetesClientException.java:129)
	at io.fabric8.kubernetes.client.KubernetesClientException.launderThrowable(KubernetesClientException.java:122)
	at io.fabric8.kubernetes.client.dsl.internal.OperationSupport.restCall(OperationSupport.java:718)
	at io.fabric8.kubernetes.client.impl.BaseClient.getApiGroups(BaseClient.java:292)
	at io.fabric8.kubernetes.client.impl.BaseClient.hasApiGroup(BaseClient.java:208)
	at com.redhat.devtools.intellij.common.kubernetes.ClusterHelper.isOpenShift(ClusterHelper.java:28)
	at com.redhat.devtools.intellij.kubernetes.model.client.ClientAdapter$Factory.create(ClientAdapter.kt:84)
	at com.redhat.devtools.intellij.kubernetes.model.client.ClientAdapter$Factory.create(ClientAdapter.kt:67)
	at com.redhat.devtools.intellij.kubernetes.model.client.ClientAdapter$Factory.create$default(ClientAdapter.kt:59)
	at com.redhat.devtools.intellij.kubernetes.model.AllContexts$2.invoke(AllContexts.kt:86)
	at com.redhat.devtools.intellij.kubernetes.model.AllContexts$2.invoke(AllContexts.kt:86)
	at com.redhat.devtools.intellij.kubernetes.model.AllContexts$client$1.invoke(AllContexts.kt:97)
	at com.redhat.devtools.intellij.kubernetes.model.AllContexts$client$1.invoke(AllContexts.kt:95)
	at com.redhat.devtools.intellij.kubernetes.model.util.ResettableLazyProperty.get(ResettableLazyProperty.kt:30)
	at com.redhat.devtools.intellij.kubernetes.model.AllContexts.getAll(AllContexts.kt:112)
	at com.redhat.devtools.intellij.kubernetes.model.AllContexts.getCurrent(AllContexts.kt:103)
	at com.redhat.devtools.intellij.kubernetes.model.ResourceModel.getCurrentContext(ResourceModel.kt:94)
	at com.redhat.devtools.intellij.kubernetes.tree.OpenShiftStructure.canContribute(OpenShiftStructure.kt:184)
	at com.redhat.devtools.intellij.kubernetes.tree.TreeStructure.getValidContributions(TreeStructure.kt:122)
	at com.redhat.devtools.intellij.kubernetes.tree.TreeStructure.createDescriptor(TreeStructure.kt:106)
	at com.intellij.ui.tree.StructureTreeModel$Node.<init>(StructureTreeModel.java:461)
	at com.intellij.ui.tree.StructureTreeModel.getValidRoot(StructureTreeModel.java:397)
	at com.intellij.ui.tree.StructureTreeModel.getRoot(StructureTreeModel.java:314)
	at com.intellij.ui.tree.StructureTreeModel.getRoot(StructureTreeModel.java:37)
	at com.intellij.ui.tree.AsyncTreeModel$CmdGetRoot.computeNode(AsyncTreeModel.java:518)
	at com.intellij.ui.tree.AsyncTreeModel$Command.computeNode(AsyncTreeModel.java:490)
	at com.intellij.util.concurrency.Invoker$Task.run(Invoker.java:381)
	at com.intellij.openapi.progress.impl.CoreProgressManager.lambda$runProcess$2(CoreProgressManager.java:217)
	at com.intellij.openapi.progress.impl.CoreProgressManager.lambda$executeProcessUnderProgress$13(CoreProgressManager.java:660)
	at com.intellij.openapi.progress.impl.CoreProgressManager.registerIndicatorAndRun(CoreProgressManager.java:735)
	at com.intellij.openapi.progress.impl.CoreProgressManager.computeUnderProgress(CoreProgressManager.java:691)
	at com.intellij.openapi.progress.impl.CoreProgressManager.executeProcessUnderProgress(CoreProgressManager.java:659)
	at com.intellij.openapi.progress.impl.ProgressManagerImpl.executeProcessUnderProgress(ProgressManagerImpl.java:79)
	at com.intellij.openapi.progress.impl.CoreProgressManager.runProcess(CoreProgressManager.java:202)
	at com.intellij.util.concurrency.Invoker.startTask(Invoker.java:236)
	at com.intellij.util.concurrency.Invoker.invokeSafely(Invoker.java:194)
	at com.intellij.util.concurrency.Invoker.lambda$offerSafely$0(Invoker.java:177)
	at com.intellij.util.concurrency.Invoker$Background.lambda$offer$0(Invoker.java:508)
	at com.intellij.util.concurrency.BoundedTaskExecutor.doRun(BoundedTaskExecutor.java:244)
	at com.intellij.util.concurrency.BoundedTaskExecutor.access$200(BoundedTaskExecutor.java:30)
	at com.intellij.util.concurrency.BoundedTaskExecutor$1.executeFirstTaskAndHelpQueue(BoundedTaskExecutor.java:222)
	at com.intellij.util.ConcurrencyUtil.runUnderThreadName(ConcurrencyUtil.java:218)
	at com.intellij.util.concurrency.BoundedTaskExecutor$1.run(BoundedTaskExecutor.java:210)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	at java.base/java.util.concurrent.Executors$PrivilegedThreadFactory$1$1.run(Executors.java:702)
	at java.base/java.util.concurrent.Executors$PrivilegedThreadFactory$1$1.run(Executors.java:699)
	at java.base/java.security.AccessController.doPrivileged(AccessController.java:399)
	at java.base/java.util.concurrent.Executors$PrivilegedThreadFactory$1.run(Executors.java:699)
	at java.base/java.lang.Thread.run(Thread.java:840)
Caused by: java.io.IOException: api.rhamilto.devcluster.openshift.com
	at io.fabric8.kubernetes.client.dsl.internal.OperationSupport.waitForResult(OperationSupport.java:504)
	at io.fabric8.kubernetes.client.dsl.internal.OperationSupport.handleResponse(OperationSupport.java:524)
	at io.fabric8.kubernetes.client.dsl.internal.OperationSupport.restCall(OperationSupport.java:711)
	... 47 more
Caused by: java.net.UnknownHostException: api.rhamilto.devcluster.openshift.com
	at java.base/java.net.InetAddress$CachedAddresses.get(InetAddress.java:801)
	at java.base/java.net.InetAddress.getAllByName0(InetAddress.java:1533)
	at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1385)
	at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1306)
	at okhttp3.Dns$1.lookup(Dns.java:40)
	at okhttp3.internal.connection.RouteSelector.resetNextInetSocketAddress(RouteSelector.java:185)
	at okhttp3.internal.connection.RouteSelector.nextProxy(RouteSelector.java:149)
	at okhttp3.internal.connection.RouteSelector.next(RouteSelector.java:84)
	at okhttp3.internal.connection.StreamAllocation.findConnection(StreamAllocation.java:215)
	at okhttp3.internal.connection.StreamAllocation.findHealthyConnection(StreamAllocation.java:135)
	at okhttp3.internal.connection.StreamAllocation.newStream(StreamAllocation.java:114)
	at okhttp3.internal.connection.ConnectInterceptor.intercept(ConnectInterceptor.java:42)
	at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:147)
	at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:121)
	at okhttp3.internal.cache.CacheInterceptor.intercept(CacheInterceptor.java:93)
	at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:147)
	at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:121)
	at okhttp3.internal.http.BridgeInterceptor.intercept(BridgeInterceptor.java:93)
	at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:147)
	at okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(RetryAndFollowUpInterceptor.java:127)
	at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:147)
	at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.java:121)
	at okhttp3.RealCall.getResponseWithInterceptorChain(RealCall.java:257)
	at okhttp3.RealCall$AsyncCall.execute(RealCall.java:201)
	at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1136)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:635)
	... 1 more

Expected result:
The toolking window should list the existing contexts and the current context should show the error that happened when trying to connect to the cluster.

[adietish]

At least one can "heal" the situation without restarting the plugin: one can change the current context using oc/kubectl and the tool windows lists the contexts again.