Disable create button after successful bucket creation (#2241)

* disable create button after creation

* disable create button after creation

Author: elharo

plugins/com.google.cloud.tools.eclipse.dataflow.ui/src/com/google/cloud/tools/eclipse/dataflow/ui/preferences/RunOptionsDefaultsComponent.java

@@ -347,6 +347,7 @@ public void widgetSelected(SelectionEvent event) {
       if (result.isSuccessful()) {
         messageTarget.setInfo("Created staging location at " + stagingLocation);
         setPageComplete(true);
+        createButton.setEnabled(false);
       } else {
         messageTarget.setError("Could not create staging location at " + stagingLocation);
         setPageComplete(false);