mxqd: Enforce minimum job runtime of 30 seconds

mxqd.c

@@ -1081,6 +1081,13 @@ int reaper_process(struct mxq_server *server,struct mxq_group_list *glist, struc
     }
     gettimeofday(&now, NULL);
     timersub(&now, &job->stats_starttime, &realtime);
+
+    if (realtime.tv_sec<30) {
+        int wait=30-realtime.tv_sec;
+        mx_log_warning("user process finished to fast (%ld seconds) : delaying termination for %d seconds",realtime.tv_sec,wait);
+        sleep(wait);
+    }
+
     res = getrusage(RUSAGE_CHILDREN, &rusage);
     if (res < 0) {
         mx_log_err("reaper: getrusage: %m");