Expose verbosity level in migrations

[Andrew]

It would be especially helpful with data migrations if one could print status/progress information depending on the "verbosity" option specified with the management command. The management command already prints to console, so this would let custom migration operations do the same thing. For some data migrations, it's useful to log custom status information, but you don't always want this displayed every time (e.g. when setting up a test database).

Perhaps verbosity-level could be passed to RunPython callbacks as an optional argument? Or perhaps the Migration object could expose some sort of logging functionality?

[Tim Graham]

I guess we could give this a try though passing verbosity all the way from the management command to the migration operations may be a bit ugly.