oopTests: Use monkeypatch for changing idle time

Change-Id: I66038dc301bc964e8d97f16ed39d4f1ec57a6dca
Signed-off-by: Yeela Kaplan <ykaplan@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/36337
Reviewed-by: Dan Kenigsberg <danken@redhat.com>