MetricsService composed of TimerService instead of inheriting

This makes testing easier. Also, passing reactor and log to the instance
for better testing
test fix after log change
removed type directive - thanks @radix
No, should be an Effect with ParallelEffects *intent*
Make the tests pass
Oops, also fix these other tests
Merge pull request #775 from rackerlabs/parallel-effects-is-an-intent

`ParallelEffects` is an intent, not an effect
Merge pull request #744 from rackerlabs/metrics_continue_on_err

Metrics service continues on error
Fix RCv3 worker docs
BY FIBER BE PURGED

Closes #757.
Merge pull request #781 from rackerlabs/remove-unused-rcv3-steps

Remove unused singular RCv3 step
Merge pull request #779 from rackerlabs/fix-rcv3-docs

Fix RCv3 worker docs
Use mock log in the test
Replace TODO with an actual test
Can't test log here: depends on context!
test_execute_delete_calls_delete_worker
test_execute_config_auths
test_execute_delete_auths
test_scrub_metadata
Bag it and tag it for the issue tracker

Closes #752.