upgrade_unified: fix for nicless and bridges with vnics

The upgrade script had a mistake when dealing with bridged networks
that made it not consider bridgeless networks nor bridges that had
vnics on them.

This bug would have made that a bridge with nic eth2 and several
vnics would have setup a network targetting:
'eth2vnet0vnet1'

Change-Id: I979ad260e86865fc7ca9760d58765e4bf0c14c3c
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28354
Reviewed-by: Dan Kenigsberg <danken@redhat.com>