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

doc/source/deploy/apache-mod-wsgi.rst

@@ -0,0 +1,49 @@
+..
+      Except where otherwise noted, this document is licensed under Creative
+      Commons Attribution 3.0 License.  You can view the license at:
+
+          https://creativecommons.org/licenses/by/3.0/
+
+
+Installing API behind mod_wsgi
+==============================
+
+#. Install the Apache Service::
+
+    Fedora 21/RHEL7/CentOS7:
+      sudo yum install httpd
+
+    Fedora 22 (or higher):
+      sudo dnf install httpd
+
+    Debian/Ubuntu:
+      apt-get install apache2
+
+#. Copy ``etc/apache2/watcher.conf`` under the apache sites::
+
+    Fedora/RHEL7/CentOS7:
+      sudo cp etc/apache2/watcher /etc/httpd/conf.d/watcher.conf
+
+    Debian/Ubuntu:
+      sudo cp etc/apache2/watcher /etc/apache2/sites-available/watcher.conf
+
+#. Edit ``<apache-configuration-dir>/watcher.conf`` according to installation
+   and environment.
+
+   * Modify the ``WSGIDaemonProcess`` directive to set the ``user`` and
+     ``group`` values to appropriate user on your server.
+   * Modify the ``WSGIScriptAlias`` directive to point to the
+     watcher/api/app.wsgi script.
+   * Modify the ``Directory`` directive to set the path to the Watcher API
+     code.
+   * Modify the ``ErrorLog and CustomLog`` to redirect the logs to the right
+     directory.
+
+#. Enable the apache watcher site and reload::
+
+    Fedora/RHEL7/CentOS7:
+      sudo systemctl reload httpd
+
+   Debian/Ubuntu:
+    sudo a2ensite watcher
+    sudo service apache2 reload