Add option to make the self label uniform when using a load balancer

[lphuberdeau]

Implements #230

Changes from the proposed spec:

• Using RABBIT_CONNECTION instead of RABBITMQ_CONNECTION as it seemed to fit better with the conventions in use.
• The self label is not removed, only uniformly set as "lb". Removing it entirely required more complex changes.

[kbudde]

Hello @lphuberdeau ,
Thank you for this change. I really enjoy the simplicity.

Only a small thing needs to be changed: Please set self label to "lb" instead of "1".

BR

[lphuberdeau]

Thanks for the quick feedback and the detailed feature proposal.