Issue 24 - Pass credentials to ua via the request object instead of the credentials method

This makes the check backward compatible with RabbitMQ 2.x as the port of 55672 gets
redirected to 15672 later in the request and thus doesn't match the hostname-port combination
that is set in the credentials method.
Merge pull request #41 from pkill/issue-24-cred-passing

Issue 24 - Pass credentials to ua via the request object instead of the ...