tests: execCmd stress test is not broken now

Since commit ce66d754, utils.execCmd stress tests should always succeed.

Change-Id: I77627254e0d832e8f496f1399ff7150b94234014
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28425
Reviewed-by: Dan Kenigsberg <danken@redhat.com>