XD-1591: Flatten out ephemeral nodes

Containers that write out ephemeral nodes indicating deployment
of a module previously used the following node structure
for streams:

/xd/deployments/streams/<name>/<type>/<label>/<container>

This has been modified to look like this:

/xd/deployments/streams/<name>/<type>.<label>.<container>

This change will make it easier to create ZooKeeper watches
on the stream to detect the addition/removal of modules
and thus calculate the state of the stream.

Addressed review comments