Fix failure to load storage plugin

Watcher fails to load storage plugin in case there is no installed
Cinder in OpenStack services.

This patch set adds collector_plugins parameter under collector
section in watcher.conf. If plugin name is in collector_plugins,
The plugin is loaded.

Change-Id: Ie3c3543216c925d49b772bf5fe3773ca7d5ae437
Closes-Bug: #1707603

watcher/conf/__init__.py

@@ -24,6 +24,7 @@ from watcher.conf import applier
 from watcher.conf import ceilometer_client
 from watcher.conf import cinder_client
 from watcher.conf import clients_auth
+from watcher.conf import collector
 from watcher.conf import db
 from watcher.conf import decision_engine
 from watcher.conf import exception
@@ -58,3 +59,4 @@ ceilometer_client.register_opts(CONF)
 neutron_client.register_opts(CONF)
 clients_auth.register_opts(CONF)
 ironic_client.register_opts(CONF)
+collector.register_opts(CONF)

watcher/conf/collector.py

@@ -0,0 +1,37 @@
+# Copyright (c) 2017 NEC Corporation
+#
+# 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 oslo_config import cfg
+
+
+collector = cfg.OptGroup(name='collector',
+                         title='Defines the parameters of '
+                         'the module model collectors')
+
+COLLECTOR_OPTS = [
+    cfg.ListOpt('collector_plugins',
+                default=['compute'],
+                help='The cluster data model plugin names'),
+]
+
+
+def register_opts(conf):
+    conf.register_group(collector)
+    conf.register_opts(COLLECTOR_OPTS,
+                       group=collector)
+
+
+def list_opts():
+    return [('collector', COLLECTOR_OPTS)]