[zk-runtime] Uniquely identify deployed modules

**Note:** this pull request is for `zk-runtime`, *not* `master`.

`ContainerRegistrar` maintains a map of deployed modules via `ModuleDescriptor.Key`. The key uses module type and label to identify a module. This prevents the tracking of multiple modules of the same type and label for different streams.

One of the problems this causes is the inability to undeploy a module for a stream if a previous stream had the same module label and type undeployed before it.

This fix introduces the stream name to the key in order to correctly identify the module runtime instance.