configure-rabbitmq: Use rabbitmqctl await_online_nodes.

rabbitmqctl ping only checks that the Erlang process is registered
with epmd.  There’s a window after that where the rabbit app is still
starting inside it.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

scripts/setup/configure-rabbitmq

@@ -19,10 +19,14 @@ RABBITMQ_PASSWORD=$("$(dirname "$0")/../get-django-setting" RABBITMQ_PASSWORD)
 
 # Wait for RabbitMQ to start up
 retries=29
-while ! "${sudo[@]}" rabbitmqctl ping -q 2>/dev/null; do
+# Could use rabbitmqctl await_startup when we upgrade to 3.7.11.
+while ! "${sudo[@]}" rabbitmqctl -q await_online_nodes 1 2>/dev/null; do
+    if ((retries == 29)); then
+        echo "Waiting for RabbitMQ to start up..."
+    fi
     sleep 1
     if ! ((retries -= 1)); then
-        "${sudo[@]}" rabbitmqctl ping -q
+        "${sudo[@]}" rabbitmqctl -q await_online_nodes 1
         break
     fi
 done