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