Change action-get help to get action info by ID
Change action-get help to get action info by ID

This changes inprove the help for action-get in order to
indicate that you can query an action using the ID too.

Change-Id: I74900fec16f05965df6ae45b9631e73b80f5c444
Depends-On: I8ce55c0eb1cab7581ba719fbbb6be7b7dced27e0
Implements: blueprint mistral-actions-identifier

openstack/python-mistralclient,openstack/python-mistralclient,StackStorm/python-mistralclient,StackStorm/python-mistralclient