Change onos-uninstall to use 'stop' rather than 'service'.

All other commands currently use 'start/stop/status'.

ONOS-2417.

Ported from onos-1.2 branch.

Change-Id: I902da5b207ec3ca5809d6ae377d8b09ae1f6eeab
(cherry picked from commit 8d6b1ca8)

@@ -9,6 +9,6 @@
 remote=$ONOS_USER@${1:-$OCI}
 
 ssh $remote "
-    sudo service onos stop 1>/dev/null 2>/dev/null
+    sudo stop onos 1>/dev/null 2>/dev/null
     sudo rm -fr $ONOS_INSTALL_DIR
 "