support user defined connection name

[norman shen]

Right now connection name for rabbitmq is determined by combination of `program name`, `pid` and `connection id`, but it would be better to have a more meaningful name.

For example, openstack helm will test pod liveliness/readiness by sending and receiving messaging to rabbitmq. The issue is that it is hard to differentiate between different `health-probe.py` when rabbitmq's log file are rolling quickly.

it would be nice to have a way to manually define a connection name by user.