First steps towards aurora client v2

First step towards aurora client v2!

- Initial implementation of the noun/verb command and options processing framework.
- Initial implementation of a command processing context for aurora commands.
- Implementations of a "Job" noun and "create" and "kill" verbs.
- Tests.

Note: not all of the v1 tests for the create and kill verbs have been migrated to the new
framework; command processing contexts need a bit more work to make it easy to do the
appropriate mocking/stubbing to support them. They'll be in the next change.

Reviewed at https://reviews.apache.org/r/16130/