[FIXED JENKINS-6623] normal return from the launch method does not ne…

…cessarily signify the success.

(even though this is arguably a poor design)

plugin/src/main/java/hudson/plugins/virtualbox/VirtualBoxComputerLauncher.java

@@ -82,7 +82,7 @@ protected boolean delegateLaunch(SlaveComputer computer, TaskListener listener)
       log(listener, "Starting stage 2 launcher (" + delegate.getClass().getSimpleName() + ")");
       getCore().launch(computer, listener);
       log(listener, "Stage 2 launcher completed");
-      return true;
+      return computer.isOnline();
     } catch (IOException e) {
       log(listener, "Unable to launch: " + e.getMessage());
       return false;