Add support to changing the Rabbitmq password on update

Add support to changing the Rabbitmq password on update

Rabbitmq Password is set on the fresh deployment, but during
update, if the password is changed, it is modified in all config
files including rabbitmq config. But the rabbitmq connection fails
because the new password is not successful applied to rabbitmq.
Setting the rabbitmq_user will invoke 'rabbitmqctl change_password'.

Scenario: The password change is applied on Step1 when configuring
Rabbitmq. Other services may be updated on different Steps. Till
other services config is updated with new rabbitmq password, and
restarted, the connections will get Access Denied response. It has
cyclic dependency. So the passwords will be changes at Step1 and
once all services are updated, the connections will work as is.

Partial-Bug: #1611704
Change-Id: I44865af3d5eb2d37eb648ac7227277e86c8fbc54