Fixes from testing

hooks/cinder_hooks.py

@@ -2,6 +2,7 @@
 
 import os
 import sys
+import json
 
 from cinder_utils import (
     ensure_ceph_pool,
@@ -90,8 +91,10 @@ def storage_backend(rel_id=None):
     if 'ceph' not in CONFIGS.complete_contexts():
         log('ceph relation incomplete. Peer not ready?')
     else:
-        relation_set(relation_id=rel_id,
-                     subordinate_configuration=CephSubordinateContext())
+        relation_set(
+            relation_id=rel_id,
+            subordinate_configuration=json.dumps(CephSubordinateContext()())
+        )
 
 
 if __name__ == '__main__':

metadata.yaml

@@ -7,10 +7,14 @@ description: |
  This charm provides a Ceph storage backend for Cinder
 categories:
   - miscellaneous
+subordinate: true
 provides:
   storage-backend:
     interface: cinder-backend
     scope: container
 requires:
+  juju-info:
+    interface: juju-info
+    scope: container
   ceph:
     interface: ceph-client

revision

@@ -1 +1 @@
-1
+2