engine: Disable support for LinuxBridge plugin

The Linux Bridge plug-in is deprecated in the Havana release,
and will be removed in the Icehouse release. Therefore the
engine should not support it.

Therefore it should be removed from the ovirt-integration as
well.

Change-Id: Iaa05188a5cba9987754058b2492329a6134e52e4
Bug-Url: https://bugzilla.redhat.com/1102018
Signed-off-by: Moti Asayag <masayag@redhat.com>