title: Check if container exists when using Kubernetes plugin for jenkins
body: <p>Our pipeline by default tries to use a container that matches the name of the current stage.
  If this container doesn't exist, the container 'default' is used.
  This functionality works but the problem is that when the container that matches the name of the stage doesn't exist, a ProtocolException occurs, which isn't catchable because it is thrown by a thread that is out of our control.
  Is there a way to check if a container actually exists when using the Kubernetes plugin for Jenkins to prevent this exception from appearing? It seems like a basic function but I haven't been able to find anything like this online.</p>
  <p>I can't show the actual code but here's a pipeline-script example extract that would trigger this exception:</p>
  <pre><code>node(POD_LABEL)
          stage('Check Version (Maven)') {
              container('containerThatDoesNotExist'}{
                  try{
                      sh 'mvn --version'
                  }catch(Exception e){
                      // catch Exception
                  }
          }
  </code></pre>
  <pre><code>java.net.ProtocolException: Expected HTTP 101 response but was '400 Bad Request'
      at okhttp3.internal.ws.RealWebSocket.checkResponse(RealWebSocket.java:229)
      at okhttp3.internal.ws.RealWebSocket$2.onResponse(RealWebSocket.java:196)
      at okhttp3.RealCall$AsyncCall.execute(RealCall.java:203)
      at okhttp3.internal.NamedRunnable.run(NamedRunnable.java:32)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
      at java.lang.Thread.run(Thread.java:748)
  </code></pre>