ifcfg: stop leaving leftover bridges when removing bonded networks

When having a network bridged non-vlanned bonded network, removing
the network while intending to remove the bond would remove the
network bridge and then create it again.

This patch fixes it by removing the 'BRIDGE' entry from the bond
before ifuppin it up again.

Change-Id: I3de692c7f089d6a9f404c3a2f6f568c12d8a985d
Bug-Url: https://bugzilla.redhat.com/1071398
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/25203
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>