Move the unthrottle tasks into the backup sub-package next to their tests.
Spread out nightly tasks to run less concurrently.
Make flake8 happy
Replace iso8601.UTC with pytz.UTC everywhere.
Order/group imports
Use Redis as the default local celery queue.

The tests depend on a running Redis instance as well now.
Refactor heka test setup and configuration parsing.

This removes the awkward konfig file stream merging code, that didn't
actually work in practice. It also introduces an explicit test-only
heka configuration file, so we avoid the need to clobber the heka
client.