Added logging of major job actions.

[dkfellows]

This logs:

• Creation (including all arguments)
• Destruction (including reason if present)
• Changes of power status of boards

The log is written to spalloc_jobs.log in the current directory, with a daily file rollover (as this is production information logging).

We might wish to look at other ways to configure logging; if we do this, the log I'm using is called jobs inside the Python logging system.

[dkfellows]

This appears to be failing because it is picking up the wrong version of SpiNNMan. The failure isn't in the code that I modified…

[coveralls]

Coverage remained the same at 100.0% when pulling 5392bfed85ef7f86c18c8d6ce30f9e5d635175a5 on job-logging into 124c87a19bf32ef923704816703e9d38972750cf on master.