mom: Require latest mom

Latest mom build uses strings for the balloon info,
needed for proper ballooning integration.

This patch will make vdsm depending on the latest mom
supporting the strings api.

Change-Id: I625a92c2ed0e67da01b7bf66a3c04c1c4de0f9fe
Signed-off-by: Doron Fediuck <dfediuck@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/17508
Reviewed-by: Dan Kenigsberg <danken@redhat.com>