Switch to eventloop model

Having a channel per event type means happy async event handling without any state machine assumptions.

Also includes a bugfix where both mesos and gozer were defining routes on the default mux. mesos now has its own http handler instead.
Basically, you're racing the waitgroup and the registration with the master.  While this race is very small, it is still there.

I solved this by introducing a state machine for the mesos subsystem, where the subsystem is not ready until this endpoint is up and serving healthy.