Suppress error messages from systemctl.

We call systemctl to see if systemd will run mdmon for us.
If it cannot, we run mdmon directly, so we aren't interested
in the error message.
So redirect stderr to /dev/null.

Signed-off-by: NeilBrown <neilb@suse.de>

util.c

@@ -1745,6 +1745,11 @@ int start_mdmon(char *devnm)
 			else
 				skipped = 0;
 
+		/* Don't want to see error messages from systemctl.
+		 * If the service doesn't exist, we start mdmon ourselves.
+		 */
+		close(2);
+		open("/dev/null", O_WRONLY);
 		snprintf(pathbuf, sizeof(pathbuf), "mdmon@%s.service",
 			 devnm);
 		status = execl("/usr/bin/systemctl", "systemctl", "start",