Run Watcher-API behind mod-wsgi

This patch adds support to run watcher-api
with mod-wsgi. It provides
1. wsgi app script files, to run watcher-api under apache.
2. updated devstack plugin to run watcher-api default with
   mod-wsgi.
3. Document to deploy watcher-api behind wsgi.

Change-Id: I8f1026f0b09fd774376220c2d117ee66f72421b8
Closes-Bug: #1675376

etc/apache2/watcher

@@ -0,0 +1,33 @@
+# 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.
+
+# This is an example Apache2 configuration file for using
+# Watcher API through mod_wsgi
+Listen 9322
+
+<VirtualHost *:9322>
+    WSGIDaemonProcess watcher-api user=stack group=stack processes=2 threads=2 display-name=%{GROUP}
+    WSGIScriptAlias / /opt/stack/watcher/watcher/api/app.wsgi
+    WSGIProcessGroup watcher-api
+
+    ErrorLog /var/log/httpd/watcher_error.log
+    LogLevel info
+    CustomLog /var/log/httpd/watcher_access.log combined
+
+    <Directory /opt/stack/watcher/watcher/api>
+        WSGIProcessGroup watcher-api
+        WSGIApplicationGroup %{GLOBAL}
+        AllowOverride All
+        Require all granted
+    </Directory>
+</VirtualHost>
+