deploy / undeploy / update on the ControlledDynamicWebAppCluster

This works & tested.  However, need to discuss the following

=> resize etc the cluster.  Currently, the war will not propagate to new cluster members.  We should at least store the URL from where it was fetched and auto-push. 
=> are there any subclasses (Cluster of ...) that need these as well?
=> What if the war file at the URL changes? or vanishes?  what is the predictble behavior?
code below is fine.  could also do functional-style using `EntityPredicates` as:

    clusterMembers = MutableList.copyOf(
        Iterables.filter(getCluster().getChildren(), Predicates.and(
             Predicates.instanceOf(JavaWebAppSoftwareProcess.class,
             EntityPredicates.attributeEqualTo(SERVICE_STATE, Lifecycle.RUNNING)
    ))));