Using MapCounters, retiring Matrix.
Using MapCounters for vtgate topo counts.
Not forking mysql to execute an admin command any more.

Or it fails with a credential server. It means we have to export
the dba queries out of mysqlctl, not a big deal.
rowcache tweaks

Don't allow rowcache without strict mode
Start invalidator after schema is initialized
Reword strict mode description
Merge branch 'rowcache'