Switch to using a tcp connection to stagger
Switch to using a tcp connection to stagger

ipc connection is problematic in many ways to use as a default:

* Permission issues if there are multiple users
* Should really use /run not /tmp, but /run isn't guaranteed to exist, and the user probably can't write to it by default
* Generating the 'unique' file name wasn't correct

I'm making use of the new ZMQ_LAST_ENDPOINT functionality in zmq 3.2

In future this should be configurable
pusher/stagger-ruby-em