misc: use utils.persist/unpersist instead of execcmd

Change-Id: Iab3e43b3f55ff562c35ceaf6ff83cf48119842be
Signed-off-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34076
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>