Use secret parameter for rabbit_password

Rabbit_password configuration was not using secret parameter so it
was visible on the logs.

Change-Id: Idad892f0c461fce53eaa81ec8a7f3cfe871a9d00
Closes-Bug: 1328448
(cherry picked from commit cbac8130da6732a1e8ad1dbcf9aec6ba75b7c20d)