Refactor duplicated #log method

As an exercise and an introduction, @vipulnsward and I picked some low-hanging fruit (according to Code Climate).

For this one, there is one behavioral change, in that the logger will now log `[JOBS::EXPORTER]` rather than `[EXPORTER]`. We discussed using `demodulize` but decided to leave it as-is. Tests were not changed as logging was explicitly stubbed in the corresponding `Jobs` specs.

The work was done so we figured we might as well open the PR. Feedback is more than welcome.