No need to push our rabbit user/pass to rabbit cookbook

Because the rabbit user/pass is stored in internal user database,
no need to push them to rabbit cookbook and expose them in config file.
And configuring rabbitmq default password with clear test is insecure,
so remove it.

Change-Id: Iab95e2dc8cd28b4a45574cf8883f1626dc332db0
Closes-Bug: #1381343