ENG-4586: Refactor: separate DR-specific stats collection work from
generic stats messaging code.
ENG-4586: Make the number of tables returned for the stat selector
flexible, albeit super-fragile.
ENG-4586: Start adding SNAPSHOTSTATUS to non-blocking stats collection
ENG-4586: Make test stop pretending to aggregate multiple stats
agents.  That much broken probably with IV2.
ENG-4586: Final bits:
- Make @SnapshotStatus redirect to the right @Statistics call
- Make old @SnapshotStatus sysproc fail hard (can't easily get rid of it as
long as the user can call @SnapshotStatus)
- Add SNAPSHOTSTATUS selector to statistics in SQLCommand
- Add a test that demonstrates a successful fix
ENG-4586: Review fixes:
- Add missing test assertions
- Delete stale SnapshotStatus sysproc IDs
Merge pull request #480 from VoltDB/eng4586

Eng4586: Fix @SnapshotStatus, r=ssantoro
schemachange app: fix assert if table has less that 100 rows
Confusion reduction: rename catalogId to siteId.  It's always been siteIds.
CatalogId made more sense when that was the type of the value that
came out of the catalog (when we got the siteId out of the catalog),
but now it just misleads the reader into thinking it actually has
something to do with the catalog.
Comments unreadable.  Fix.
Merge branch 'master' into notest-ENG-4389-outputschema-less
ENG-4389 WIP -- still a little heavy