Add Cinder API wsgi application

Add Cinder API wsgi application

This change adds cinder API application, so cinder API can be run
under wsgi server(Apache, Nginx, etc). Eventlet will still be used
by default.

Cinder API with eventlet as a webserver and wsgi application
managing has some cons:

* Cinder API is deployed in other way as a common web application.
Apache/Nginx is generally used web servers for REST API application.

* Cinder API is run as a separate service. It means that cloud
operators need to configure some software to monitor that the API
is running.

* Apache/Nginx works better under the real heavy load than eventlet.

To use c-api deployment under Apache in devstack assign
devstack var CINDER_USE_MOD_WSGI="True".
Related changes in devstack:
 https://review.openstack.org/#/c/204643/

Cinder documentation on how deploy cinder API under Apache:
 https://review.openstack.org/#/c/207020/

Patch for Infra to make it tested:
 https://review.openstack.org/#/c/208498/

DocImpact
Implements: blueprint: non-eventlet-wsgi-app

Change-Id: If877d700b0efaa5406efa8f8f17c5816928e83ce