Adding provides.py for openstack-integrator relation.

This change is to be able to provide keystone-credentials interface by
openstack-integrator charm. Openstack-integrator already has credentials
from keystone (sitting in the other model) from 'juju trust' or
charm config.

So it can expose them to kubernetes-master units directly in
keystone-credentials relation. This way we can reuse the existing
keystone from openstack model to authenticate users in k8s-dashboard etc.

Change-Id: I6ecc32d24305205ce3b11f047658bd056f5960a6

provides.py

@@ -0,0 +1,35 @@
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from charms.reactive import RelationBase
+from charms.reactive import hook
+from charms.reactive import scopes
+
+
+class KeystoneProvides(RelationBase):
+    scope = scopes.GLOBAL
+
+    @hook('{provides:keystone-credentials}-relation-joined')
+    def joined(self):
+        self.set_flag('{relation_name}.connected')
+
+    @hook('{provides:keystone-credentials}-relation-{broken,departed}')
+    def departed(self):
+        self.clear_flag('{relation_name}.connected')
+
+    def expose_credentials(self, credentials):
+        """Expose Keystone credentials to related units.
+
+        :param credentials: The Keystone credentials to be exposed.
+        :type credentials: dict
+        """
+        self.set_remote(**credentials)