utils: change persistFile to persist

For style reasons. This way it's compatible with other
calls in the utils module.

Change-Id: I54cabe8976713169755933958d183eefbd4fac88
Signed-off-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34073
Reviewed-by: Yaniv Bronhaim <ybronhei@redhat.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>