vdsm-toolize dummybr and nwfilter

Move dummybr and nwfilter to vdsm-tool, so that all the init wrappers in
the supported or to-be-supported systems can call them uniformly.

Change-Id: Id32554824cc231f428523dbd34a3fa189b361ae5
Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/15370
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>