Right now, mongobridge and its javascript helpers allows it only to effectively manage traffic between mongodb server processes. We sometimes want to test scenarios where we want to manage connections between clients (i.e. mongo shell), like ensuring that servers handle situations correctly even when clients are unable to properly "hang-up" their connections. this ticket tracks instrumenting mongobridge to allow it to manage those connections and make that kind of testing easier. 

To do so we should just:

--> change the mongobridge host-identification protocol to allow processes to identify themselves exactly once to mongobridge with any hello cmd they send, not just the first. This way clients can identify themselves as proxyable  hosts.

--> add helper to the js mongobridge object to make use of this new ability + let these bridges can manage messages from hosts directly