Set firewall state to CREATED when dealing with DVR

When DVR is enabled as a default option for creating routers, firewall
resources will need to have a new initial state, so that reconciliation
can be done once all L3 agents have processed the firewall rules.

The new state has been introduced to preserve API bw compatibility
with centralized routers.

Partial-bug: #1360351
Supports-blueprint: neutron-dvr-fwaas

Change-Id: I53122570dd3a2311eedb24ccd925bcdc9ad4f70c
Merge "Set firewall state to CREATED when dealing with DVR"