L3 Agent support for routers with HA and DVR

L3 Agent support for routers with HA and DVR

The main difference for DVR HA routers is where
the VRRP/keepalived logic is run and which ports
fall in the HA domain for DVR.  Instead of running
in the qrouter namespace, keepalived will run inside
the snat-namespace.  Therefore only snat ports will
fall under the control of the HA domain.

Partial-Bug: #1365473

Change-Id: If2962580397d39f72fd1fbbc1188a6958f00ff0c
Co-Authored-By: Michael Smith <michael.smith6@hp.com>
Co-Authored-By: Hardik Italia <hardik.italia@hp.com>
Co-Authored-By: Adolfo Duarte <adolfo.duarte@hp.com>
Co-Authored-By: John Schwarz <jschwarz@redhat.com>