ENG-4528: Consolidate error response generation/sending.
ENG-4528: Pass the params we got to the collectStats() call and below.
ENG-4528: Move the argument parsing for statistics calls to
StatsAgent.  Introduce the notion of 'subselector', which is really
the old SysProcSelector.
ENG-4528: Be more explicit when we're using the subselector.  Dispatch
correcly according to top-level STATISTICS selector, even though it's
the only one right now.  Move code that will be common to
handleJSONMessage().
ENG-4528: Remove unnecessary args from dispatchStatistics()
ENG-4528: Make @SystemCatalog non-blocking in a really horrible way.
Hopefully have time to go back and refactor when @SystemInformation is
done.
- @SystemCatalog is no longer a stored proc, fix up tests which think it
  is
ENG-4528: Make @SystemInformation non-blocking in a pretty horrible
way.
- We want deduped SYSTEMINFORMATION DEPLOYMENT, so just return local results.
ENG-4528: Cleanup: Stop catching and eating Throwable.  Blindly
catching and eating all Exceptions ought to be good enough for any
man.
ENG-4528: Cleanup: Remove unnecessary throws declarations.  Fix a comment.
ENG-4528: Rename SysProcSelector to StatsSelector
ENG-4528: Introduce OpsSelector, use it rather than magic strings for
OPS dispatch.
ENG-4528: Refactoring: Create two copies of StatsAgent, one each for
SystemCatalog and SystemInformation.  Add crude construction and
mailbox registration, they currently go nowhere, do nothing.
ENG-4528: Refactor: actually dispatch SYSTEMINFORMATION and
SYSTEMCATALOG to their StatsAgent copies
ENG-4528: Refactor: delete non-StatsAgent things from StatsAgent
ENG-4528: Refactor: Remove non-SystemInformation stuff from
SystemInformationAgent
ENG-4528: Refactor: Remove non-SystemCatalog stuff from
SystemCatalogAgent
ENG-4528: Once again copy StatsAgent to OpsAgent, which will become
the base class for all of the various agents.  Strip it down to
hopefully just the stuff we care about.
ENG-4528: Move the outstanding pending requests checks until after we
parse args and check to see if we can satisfy the OPS request locally.
ENG-4528: Refactor: Make OpsAgent and StatsAgent work together in an
abstract class extension sense.  Crude, undocumented, more to come.
ENG-4528: Refactor: Turn SystemInformationAgent into a proper subclass
of OpsAgent.