XD-1960 Module deployment upon new leadership election

- Upon new leadership election, when the `ContainerListener` deploys
unallocated stream/job modules (via ArrivingContainerModuleRedeployer)
check for any existing deployments on the container in context.
 - If there are deployments on this container, then ignore the
container for unallocated module deployments given that this
container has already participated in module deployments.
 - Only caveat with this approach is that, since the
existing container may still have no deployments because of no
matching criteria, this would still run the unallocated module
deployments against this container (obviously no modules would be
deployed eventually).

This approach seems to work better than having some other logic
to compare against deployed modules of the same module type
for a given stream/job.
Here, it would probably be better to make this a boolean method (e.g. `hasDeployments(..)`). Then simply check the child count rather than getting all children:

````
Stat stat = client.checkExists().forPath(...);
return (stat != null && stat.getNumChildren() > 0);
````