Added gunicorn as server application manager

This patch adds gunicorn as dependency for starting and managing server
workers. Gunicorn allow users to chose whether to use workers based on a
sync process, eventlet or gevent. It also manages multiple workers, ssl,
process uid, process gid.

Implements blueprint transport-base

Change-Id: Ic328dbb937f8df69691911c6e6ff6b318bb1db34