modify mom functional test to use VdsProxy

This patch puts vdscli APIs in VdsProxy in utils. It modifies mom functional
test to use it instead of direct calling. It resembles the way network
functional test uses.

Change-Id: I874d527e3919c1beff328183eb12f332f2399b95
Signed-off-by: MeiLiu <liumbj@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/18271
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>