[jillr] Add nagios-external-master interface and logic so n-e-m hooks will run

hooks/percona_hooks.py

@@ -278,6 +278,9 @@ def config_changed():
         # make sure all the HA resources are (re)created
         ha_relation_joined()
 
+    if is_relation_made('nrpe-external-master'):
+        update_nrpe_config()
+
 
 @hooks.hook('cluster-relation-joined')
 def cluster_joined():

metadata.yaml

@@ -14,6 +14,9 @@ provides:
     interface: mysql-root
   shared-db:
     interface: mysql-shared
+  nrpe-external-master:
+    interface: nrpe-external-master
+    scope: container
 peers:
   cluster:
     interface: percona-cluster

unit_tests/test_percona_hooks.py

@@ -8,7 +8,9 @@ import percona_hooks as hooks
 TO_PATCH = ['log', 'config',
             'get_db_helper',
             'relation_ids',
-            'relation_set']
+            'relation_set',
+            'update_nrpe_config']
+
 
 
 class TestHaRelation(CharmTestCase):