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

devstack/files/apache-watcher-api.template

@@ -0,0 +1,42 @@
+# 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 the
+# Watcher API through mod_wsgi.  This version assumes you are
+# running devstack to configure the software.
+
+Listen %WATCHER_SERVICE_PORT%
+
+<VirtualHost *:%WATCHER_SERVICE_PORT%>
+    WSGIDaemonProcess watcher-api user=%USER% processes=%APIWORKERS% threads=1 display-name=%{GROUP}
+    WSGIScriptAlias / %WATCHER_WSGI_DIR%/app.wsgi
+    WSGIApplicationGroup %{GLOBAL}
+    WSGIProcessGroup watcher-api
+    WSGIPassAuthorization On
+
+    ErrorLogFormat "%M"
+    ErrorLog /var/log/%APACHE_NAME%/watcher-api.log
+    CustomLog /var/log/%APACHE_NAME%/watcher-api-access.log combined
+
+
+    <Directory %WATCHER_WSGI_DIR%>
+        WSGIProcessGroup watcher-api
+        WSGIApplicationGroup %{GLOBAL}
+        <IfVersion >= 2.4>
+            Require all granted
+        </IfVersion>
+        <IfVersion < 2.4>
+            Order allow,deny
+            Allow from all
+        </IfVersion>
+    </Directory>
+</VirtualHost>