Add ceph-mds relation

This relation is very similar to the ceph-client relation so add
it to this repo so they can share code. This will retire the
seperate repo *1 and also require an update to the central
index of interfaces to point at the new location.

*1 https://github.com/openstack/charm-interface-ceph-mds
*2 https://juju.github.io/layer-index/

Change-Id: I9f438bb678da1b69d8161390aad2cf58907bc1b5

ceph-mds

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+src/ceph_mds

src/ceph_mds/README.md

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+# Overview
+
+This interface layer handles the communication between the Ceph Monitor
+and a client that requires an admin key.
+
+# Usage
+
+## Requires
+
+This interface layer will set the following states, as appropriate:
+
+  * `{relation_name}.connected` The ceph client has been related to a provider.
+  * `{relation_name}.pools.available` The pools requested have been created,
+  The following accessors will be available:
+   - key - The mds cephx key
+   - admin_key - The cephx admin key
+   - auth - Whether or not strict auth is supported
+   - mon_hosts - The public addresses list of the monitor cluster
+
+
+Client example:
+
+```python
+@when('ceph-mds.connected')
+def storage_ceph_connected(ceph):
+    ceph.announce_mds_name()
+    ceph.initialize_mds(hookenv.service_name())
+
+@when('ceph-mds.pools.available')
+def ceph_connected(ceph_info):
+  charm_ceph_conf = os.path.join(os.sep, 'etc', 'ceph', 'ceph.conf')
+  cephx_key = os.path.join(os.sep, 'etc', 'ceph', 'ceph.client.admin.keyring')
+
+  ceph_context = {
+      'auth_supported': ceph_client.auth,
+      'mon_hosts': ceph_client.mon_hosts,
+  }
+
+  with open(charm_ceph_conf, 'w') as cephconf:
+    cephconf.write(render_template('ceph.conf', ceph_context))
+
+  # Write out the cephx_key also
+  with open(cephx_key, 'w') as cephconf:
+    cephconf.write(ceph_client.key)
+```

src/ceph_mds/interface.yaml

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+name: ceph-mds
+summary: Ceph MDS Client Interface
+version: 1

src/ceph_mds/lib

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+../lib

src/ceph_mds/requires.py

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+# Copyright 2020 Canonical Ltd
+#
+# 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.
+
+import socket
+
+from .lib import base_requires
+
+from charms.reactive import (
+    when,
+)
+from charmhelpers.contrib.storage.linux.ceph import (
+    CephBrokerRq,
+)
+
+
+class CephClient(base_requires.CephRequires):
+
+    ceph_pool_app_name = 'cephfs'
+
+    @when('endpoint.{endpoint_name}.joined')
+    def joined(self):
+        super().joined()
+
+    @when('endpoint.{endpoint_name}.changed')
+    def changed(self):
+        super().changed()
+
+    @when('endpoint.{endpoint_name}.departed')
+    def departed(self):
+        super().changed()
+
+    @when('endpoint.{endpoint_name}.broken')
+    def broken(self):
+        super().broken()
+
+    def fsid(self):
+        return self.all_joined_units.received.get('fsid')
+
+    def mds_key(self):
+        """Retrieve the cephx key for the local mds unit"""
+        return self.all_joined_units.received.get(
+            '{}_mds_key'.format(socket.gethostname()))
+
+    def initial_ceph_response(self):
+        data = {
+            'mds_key': self.mds_key(),
+            'fsid': self.fsid(),
+            'auth': self.auth(),
+            'mon_hosts': self.mon_hosts()
+        }
+        return data
+
+    def announce_mds_name(self):
+        for relation in self.relations:
+            relation.to_publish_raw['mds-name'] = socket.gethostname()
+
+    def request_cephfs(self, name):
+        rq = self.get_current_request() or CephBrokerRq()
+        rq.add_op({
+            'op': 'create-cephfs',
+            'mds_name': name,
+            'data_pool': "{}_data".format(name),
+            'metadata_pool': "{}_metadata".format(name)})
+        self.send_request_if_needed(rq)
+
+    def initialize_mds(self, name, replicas=3):
+        """
+        Request pool setup and mds creation
+
+        @param name: name of mds pools to create
+        @param replicas: number of replicas for supporting pools
+        """
+        self.create_replicated_pool(
+            name="{}_data".format(name),
+            replicas=replicas,
+            weight=None,
+            app_name=self.ceph_pool_app_name)
+        self.create_replicated_pool(
+            name="{}_metadata".format(name),
+            replicas=replicas,
+            weight=None,
+            app_name=self.ceph_pool_app_name)
+        self.request_cephfs(name)