mom: add mom balloon functional tests for running vms

The balloon functional test includes the grow and shrink tests.
It uses diverse policies to triger grow and shrink operation.

Change-Id: I922568233dc769d83e2fdffe1c24439d13d03d7e
Signed-off-by: MeiLiu <liumbj@linux.vnet.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/13156
Reviewed-by: Mark Wu <wudxw@linux.vnet.ibm.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>