Implements part of blueprint ssl-endpoints
Adds in configuration options:
kombu_ssl_version (ssl version)
kombu_ssl_keyfile (ssl keyfile)
kombu_ssl_certfile (ssl certfile)
kombu_ssl_ca_certs (ssl ca certfile)
This adds onto rabbit_use_ssl (which must be True for the above to have any effect) and allows
users to specify in greater detail (more than just True/False) how SSL is going to be configured.
Change-Id: I2186a6aa9397df857321324bf4007bc8310b85ce
6393c125dd