Request to merge client certificate authentication support for RabbitMQ

This pull request adds 2 features:
1) allow for setting the AuthMechanisms on the ConnectionFactory to enable client-certificate authentication
2) Allow for explicitly setting the client certificate used because my InfoSec team gets all worked up when we store certificates on disk.

The tests for #1 will break unless the server is configured for authentication through client certificates as per this blog entry:
http://blog.johnruiz.com/2011/12/establishing-ssl-connection-to-rabbitmq.html

Additionally the server will need a user created with the DN or CN of the certificate depending on the server config.