Improve shutdown for container-based arrays.

1/ close a race where multiple arrays disappear at once
   and monitor isn't woken up to find out that the last one
   has gone.
2/ "mdadm -Ss" needs to pause briefly for mdmon to exit.

managemon.c

@@ -159,6 +159,7 @@ static void remove_old(void)
 		if (pending_discard == discard_this)
 			pending_discard = NULL;
 		discard_this = NULL;
+		wakeup_monitor();
 	}
 }
 
@@ -174,7 +175,6 @@ static void replace_array(struct supertype *container,
 	 */
 	remove_old();
 	while (pending_discard) {
-		wakeup_monitor();
 		while (discard_this == NULL)
 			sleep(1);
 		remove_old();

mdadm.c

@@ -1257,6 +1257,16 @@ int main(int argc, char *argv[])
 
 							put_md_name(name);
 						}
+						/* This is a bit of a hack.
+						 * When we stop an array in a container, it
+						 * takes a moment for mdmon to let go.
+						 * So just pause briefly incase that is
+						 * happening.  Maybe we should do something
+						 * more deterministic via the socket.
+						 */
+						if (progress && err)
+							usleep(50000);
+
 					} while (!last && err);
 					if (err) rv |= 1;
 				} else {