engine:

Extended the `run_calc` interface to support the option to disable the
job supervisor (and thus, NOT fork the process).
supervising/supervisor:

Abstracted logging initialization (to the console or file) to a
separate function.
Merge pull request #1256 from larsbutler/disable-supervision

Add `engine` functionality to disable the job supervisor

[r=matley] [f=*1206913]