Fix to enable delete of firewall in PENDING_CREATE state

Firewall will in PENDING_CREATE state if there is no underlying router in the
tenant. When the router and an associated i/f is created then with a sequence
of msgs it is set to ACTIVE state by the plugin. If a delete is triggered when
in PENDING_CREATE state in such a situation, the msg was ignored - fixing this to
account for the fact that a delete makes sense in this situation so the agent
sends the appropriate msg back to the plugin so it can delete it.

Change-Id: Id1db0a8413fd815b518fe4dc57fc6277c09e7f00
Closes-Bug: #1223478
Merge "Fix to enable delete of firewall in PENDING_CREATE state"