Implemented base + moved plugins & service conf

In this changeset, I implemented the main logic although this is
mainly a shameful copy/paste of Nova's blueprint
https://blueprints.launchpad.net/nova/+spec/centralize-config-options

Partially Implements: blueprint centralise-config-opts

Change-Id: Ib645ad5da5c706336bb6ac37e85b027d05665c32

watcher/conf/plugins.py

@@ -0,0 +1,72 @@
+# -*- encoding: utf-8 -*-
+# Copyright (c) 2016 b<>com
+#
+# Authors: Vincent FRANCOISE <vincent.francoise@b-com.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.
+
+import prettytable as ptable
+
+from watcher.applier.loading import default as applier_loader
+from watcher.common import utils
+from watcher.decision_engine.loading import default as decision_engine_loader
+
+PLUGIN_LOADERS = (
+    applier_loader.DefaultActionLoader,
+    decision_engine_loader.DefaultPlannerLoader,
+    decision_engine_loader.DefaultScoringLoader,
+    decision_engine_loader.DefaultScoringContainerLoader,
+    decision_engine_loader.DefaultStrategyLoader,
+    decision_engine_loader.ClusterDataModelCollectorLoader,
+    applier_loader.DefaultWorkFlowEngineLoader,
+)
+
+
+def list_opts():
+    """Load config options for all Watcher plugins"""
+    plugins_opts = []
+    for plugin_loader_cls in PLUGIN_LOADERS:
+        plugin_loader = plugin_loader_cls()
+        plugins_map = plugin_loader.list_available()
+
+        for plugin_name, plugin_cls in plugins_map.items():
+            plugin_opts = plugin_cls.get_config_opts()
+            if plugin_opts:
+                plugins_opts.append(
+                    (plugin_loader.get_entry_name(plugin_name), plugin_opts))
+
+    return plugins_opts
+
+
+def _show_plugins_ascii_table(rows):
+    headers = ["Namespace", "Plugin name", "Import path"]
+    table = ptable.PrettyTable(field_names=headers)
+    for row in rows:
+        table.add_row(row)
+    return table.get_string()
+
+
+def show_plugins():
+    rows = []
+    for plugin_loader_cls in PLUGIN_LOADERS:
+        plugin_loader = plugin_loader_cls()
+        plugins_map = plugin_loader.list_available()
+
+        rows += [
+            (plugin_loader.get_entry_name(plugin_name),
+             plugin_name,
+             utils.get_cls_import_path(plugin_cls))
+            for plugin_name, plugin_cls in plugins_map.items()]
+
+    return _show_plugins_ascii_table(rows)