Centralize plugin loaders in watcher/applier

Refactor all plugin loaders in watcher/applier into
watcher/applier/loading/default.py.

Change-Id: I0f0a87d4f72ead45d34aca1b14219fd2ede42a6f
Closes-Bug: #1591095

watcher/applier/actions/factory.py

@@ -19,7 +19,7 @@ from __future__ import unicode_literals
 
 from oslo_log import log
 
-from watcher.applier.actions.loading import default
+from watcher.applier.loading import default
 
 LOG = log.getLogger(__name__)
 

watcher/applier/actions/loading/default.py

@@ -1,25 +0,0 @@
-# -*- 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 watcher.common.loader import default
-
-
-class DefaultActionLoader(default.DefaultLoader):
-    def __init__(self):
-        super(DefaultActionLoader, self).__init__(namespace='watcher_actions')