Cleanup floatingips also on router delete

In router remove path process_router(), processing of floating ips
is getting skipped. This change adds processing of floating ips
if the external gateway for the router was previously set. Since
DVR uses FIP namespaces and agent gateway ports, this change ensures
such ports and namespaces are removed.

Change-Id: Ib1d8fb54adcd8aab411dced695d171376687c980
Partial-bug: #1367588
Merge "Cleanup floatingips also on router delete"