Basic benchmark functionality.

Listing, aborting, and reporting added/improved. Active listing now
reports on per-node basis. Abort action reports on which nodes the abort
executed.

Modified how active benchmarks are reported to get 'live' metrics out of
running processes, rather than static data out of the cluster meta-data.
Allows us to get more accurate up-to-the-second metrics.

Simplified REST API to 3 simple commands:
- PUT : submit
- POST : abort
- GET : list

TODO:
- Proper thread pool sizing. Added BENCH pool, need to confirm what is
  appropriate size.
- Improve unit tests
- Documentation
- Better percentile calculation
- Error condition reporting
- Save benchmark status after completion for later retrieval. This
  changed due to how we now get 'live' status out of running process.
- Marvel integration?