Prepare resource broker for cancellation changes

This patch anticipates the changes to Llama that allow a
client-specified resource ID to be returned with every reservation or
expansion request. Doing this allows us to remove the tricky
coordination logic between WaitForNotification() and AMNotification()
when we don't know which side will access the rendezvous data structures
first. Now we can guarantee that the consumer-side will be set-up before
the notification is received.

Change-Id: I908b1dae8d074a84b0465e3a444d6651f126efd7
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3093
Reviewed-by: Henry Robinson <henry@cloudera.com>
Tested-by: jenkins
(cherry picked from commit 24d0c0210f1b03443ffc7cf2f53a945c7b8dd7e2)
Reviewed-on: http://gerrit.ent.cloudera.com:8080/3257