Make prometheus_rabbitmq_exporter plugin available in v3.8

In order to make this work in 3.8, we had to change the list all
available plugins output. The script that we use to list plugins was
failing because the rabbitmq-plugins list output changed in 3.8. This
might not be intentional, but it's something that we had to address
before this would work. cc @hairyhum

Author: gerhard

config/blobs.yml

@@ -86,6 +86,21 @@ rabbitmq-plugins/3.7/prometheus_rabbitmq_exporter-v3.7.2.2.ez:
   size: 215891
   object_id: e368950e-bd10-4ab5-5660-1abd32e2ce93
   sha: d6a817d8bd655b41f73c234262e785af41ed18ee
+rabbitmq-plugins/3.8/accept-0.3.3.ez:
+  size: 13397
+  sha: 44571bfe89be4eac98228a8b7d9b3afd03b4760a
+rabbitmq-plugins/3.8/prometheus-3.5.1.ez:
+  size: 200783
+  sha: ddbfa5a3b15e8c63247909c63ef88632dd31b748
+rabbitmq-plugins/3.8/prometheus_cowboy-0.1.4.ez:
+  size: 14343
+  sha: 537969b947d4ddb4166cac826e4a0a243f4e5dc7
+rabbitmq-plugins/3.8/prometheus_httpd-2.1.8.ez:
+  size: 22059
+  sha: 494e6169a833635238111cd1d3bd1c952c1fe83a
+rabbitmq-plugins/3.8/prometheus_rabbitmq_exporter-3.7.2.4.ez:
+  size: 224548
+  sha: 00061e8e7b8f836e34b831e88baeb87199c33136
 rabtap-1.11.tgz:
   size: 3067339
   object_id: fc6994ec-ece7-4cca-698a-1ef34281b46c

jobs/rabbitmq-server/templates/bin/_enable_plugins

@@ -1,14 +1,15 @@
 #!/usr/bin/env bash
 
 set -e
+set -o pipefail
 
 list_available_plugins_with_retry() {
   # Just in case RabbitMQ is booting
   # and hasn't discovered all plugins yet,
   # retry a couple of times
   for _ in {1..10}
   do
-      rabbitmq-plugins list -m && return 0 # success
+      (rabbitmq-plugins list --minimal | grep -v "Listing plugins") && return 0 # success
       sleep 1
   done
   return 1 # fail