Fix double-using the same bridge for libvirt network
Fix double-using the same bridge for libvirt network

If forward.mode == 'bridge', then specified phys_dev is used for
both:
   libvirt network, based on the bridge;
   include this phys_dev as a slave interface to the network bridge

The second action is wrong for 'bridge' mode.

Change-Id: I837972990e2bab115b96e7af42e1068dbdc6dbff

stackforge/fuel-devops,stackforge/fuel-devops