Add a common generic dynamic loader for watcher

In watcher, an audit generates a set of actions which
aims at achieving a given goal (lower energy consumption, ...).
It is possible to configure different strategies in order to achieve
each goal. Each strategy is written as a Python class which produces
a set of actions. Today, the set of possible actions is fixed for a
given version of Watcher and enables optimization algorithms to
include actions such as instance migration, changing hypervisor state,
changing power state (ACPI level, ...).

This patchset add a common generic dynamic loader for plugins,
such as for custom Actions, Strategies, Planners, etc.

Partially implements: blueprint watcher-add-actions-via-conf

Change-Id: I59d031b93865fff2540e3973921e1bdafa95f88e

watcher/decision_engine/planner/loading/default.py

@@ -0,0 +1,30 @@
+# -*- encoding: utf-8 -*-
+# Copyright (c) 2015 b<>com
+#
+# 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 __future__ import unicode_literals
+
+from oslo_log import log
+
+from watcher.common.loader.default import DefaultLoader
+
+LOG = log.getLogger(__name__)
+
+
+class DefaultPlannerLoader(DefaultLoader):
+    def __init__(self):
+        super(DefaultPlannerLoader, self).__init__(
+            namespace='watcher_planners')