Remove unused bridge interfaces
Remove unused bridge interfaces

If a network gateway of multi hosted network is unsed by any VM on the
host, we tear down it.
It is implemented only with the VLAN manager.

Fixes LP bug #1084651

Change-Id: Ia7e399de5b8ddf6ec252d38dfbb8762c4f14e3a5

n0ano/gantt,n0ano/gantt