Set availability_zone as part of the cloud-compute relation

A new Juju action, to the nova-cloud-controller charm, will be
added to sync the nova-compute units Juju availability zones with
the availability from OpenStack.

It is useful in the context of a MAAS deployment, in order to map
MAAS AZs to OpenStack AZs.

Change-Id: I62f68f0c0c97aeca20a8afb32095d2972abd8473

hooks/nova_compute_hooks.py

@@ -345,6 +345,10 @@ def compute_joined(rid=None):
             'migration', cidr_network=config('libvirt-migration-network')),
     }
 
+    juju_az = os.environ.get('JUJU_AVAILABILITY_ZONE')
+    if juju_az:
+        relation_set(relation_id=rid, availability_zone=juju_az)
+
     if migration_enabled():
         auth_type = config('migration-auth-type')
         settings['migration_auth_type'] = auth_type

unit_tests/test_nova_compute_hooks.py

@@ -383,6 +383,20 @@ class NovaComputeRelationsTests(CharmTestCase):
         hooks.compute_joined()
         self.assertFalse(self.relation_set.called)
 
+    @patch('os.environ.get')
+    def test_compute_joined_with_juju_az(self, mock_env_get):
+        def environ_get_side_effect(key):
+            return {
+                'JUJU_AVAILABILITY_ZONE': 'az1',
+            }[key]
+        mock_env_get.side_effect = environ_get_side_effect
+        self.migration_enabled.return_value = False
+        hooks.compute_joined('cloud-compute:2')
+        self.relation_set.assert_called_with(**{
+            'relation_id': 'cloud-compute:2',
+            'availability_zone': 'az1',
+        })
+
     def test_compute_joined_with_ssh_migration(self):
         self.migration_enabled.return_value = True
         self.test_config.set('migration-auth-type', 'ssh')