RM fixes to get tests passing

* One last NotifyThreadUsageChange() mismatched pair
* Don't set resource in plan fragment params if there isn't a resource
  available. This fixes the problem where if no fragment with resources
  was assigned to the same node as the coordinator, the coordinator
  would have a dummy resource allocation which didn't work with
  expansion.
* Substitute #ID in all impalad arguments to start-impala-cluster.py
  with the 0-indexed ID of the impalad being started. This is required
  to have different Impala processes use different cgroups.

Change-Id: If8c8fd8bef0809bdaf16115a45a9695fc2bf3e1b
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2047
Reviewed-by: Nong Li <nong@cloudera.com>
Tested-by: jenkins