Instrument agent

Added the following counters:

  container_create
  container_create_failure
  container_destroy
  container_start
  container_start_failure
  container_stop
  container_status_kill
  container_status_down_successful
  container_status_force_down_successful

container creations = container_create - container_create_failure
container starts = container_start - container_start_failure

The container_status were easily testable.  Sadly, the others are embedded in such a way that testing is difficult.

Intended for review by @bernerdschaefer @peterbourgon