createdb.py: Archive dump files on migrate.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit d9bf7aeee52b2398284ea39c007d7a9874525fa7)
createdb.py: Nicer archiving system on migrate, based on Will's HR dumps.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit ebce7491611d3895f8fbfca1acbd5d514bb46b0c)