Allow setting the HOSTNAME reported to the master via an env var; Stub and endpoint for tailing the log of a process assuming you know the path.

I'd like to get this log processing a bit more automatic but I need to
spend more time in Dadd's API.
Refactor the code to report success via worker.

We need to keep our final error checking as slim as possible. I had been
reporting success in the error wrapper, but that mean that if it failed
to report a success, then that simply disappeared.