Drop the invented 'DBA mode auto-commits each statement' phrasing. Use
miaoda-cli's exact rolled-back sentence 'Transaction rolled back; no
changes persisted.', and plain SQL semantics for the auto-commit case
('Earlier statements were committed and not rolled back; ...'). Update
tests and the db-execute reference doc to match.
Change-Id: Ia74190a228355f72155bc5663030152bc69e9a4e