Support hacluster using peer-availability relation

Add support for the hacluster charm to be related to a principle
using the juju-info interface using the peer-availability relation.
This is useful in the situation where a cluster without any resources
is needed.

Change-Id: Ibd03ba7923cfd2c412d5f772cf385a21c423e5af

hooks/hooks.py

@@ -229,6 +229,8 @@ def hanode_relation_joined(relid=None):
 
 @hooks.hook('ha-relation-joined',
             'ha-relation-changed',
+            'peer-availability-relation-joined',
+            'peer-availability-relation-changed',
             'hanode-relation-changed')
 def ha_relation_changed():
     # Check that we are related to a principle and that
@@ -253,7 +255,7 @@ def ha_relation_changed():
             level=INFO)
         return
 
-    relids = relation_ids('ha')
+    relids = relation_ids('ha') or relation_ids('juju-info')
     if len(relids) == 1:  # Should only ever be one of these
         # Obtain relation information
         relid = relids[0]

hooks/peer-availability-relation-changed

@@ -0,0 +1 @@
+hooks.py

hooks/peer-availability-relation-joined

@@ -0,0 +1 @@
+hooks.py

metadata.yaml

@@ -15,6 +15,9 @@ requires:
   juju-info:
     interface: juju-info
     scope: container
+  peer-availability:
+    interface: juju-info
+    scope: container
 provides:
   ha:
     interface: hacluster