Disallowing starting the executor when worker running
Disallowing starting the executor when worker running

To avoid consistency/threading/runtime issues stop the action
engine executor from being started if it is already running with
a valid worker thread.

Change-Id: I39925e55e7b171f289152d941ebdf390552f880c

pombredanne/taskflow-1,junneyang/taskflow,openstack/taskflow,jimbobhickville/taskflow,jimbobhickville/taskflow,openstack/taskflow,junneyang/taskflow,pombredanne/taskflow-1