Expose hostname in actor.statusMessage when there is an error

[mwvaughn]

When an error is encountered creating an actor, statusMessage is populated with informative detail as to what might have caused the issue. Here's an example:

"statusMessage": "Unable to start worker; error: Got exception trying to run container from image: abaco/core:0.11.0. Exception: 500 Server Error: Internal Server Error (\"devmapper: Thin Pool has 30979 free data blocks which is less than minimum required 31128 free data blocks. Create more free space in thin pool or use dm.min_free_space option to change behavior\")"

We don't easily know which Abaco host this has occurred on, which makes investigating just a bit harder than it needs to be. I suggest we consider including hostname or other identifier in statusMessage to assist in the process.