Delete useless withRelaunch argument of onReboot in vm.py

If we set the withRelaunch argument to True, it can't work normally
because function relaunch() on clientIF class isn't defined.Here, we
delete the useless argument directly to avoid potential error.

Change-Id: I53b372feca865327e9e81f1b89e6d7566038c031
Signed-off-by: jarod.w <work.iec23801@gmail.com>
Reviewed-on: http://gerrit.ovirt.org/9096
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Tested-by: Dan Kenigsberg <danken@redhat.com>