Be more specific in checking if a job restarted successfully.

Fixes: #9056

library/system/service

@@ -1287,7 +1287,7 @@ def main():
     (rc, out, err) = service.modify_service_state()
 
     if rc != 0:
-        if err and "is already" in err:
+        if err and "Job is already running" in err:
             # upstart got confused, one such possibility is MySQL on Ubuntu 12.04
             # where status may report it has no start/stop links and we could
             # not get accurate status