Don't delete south migration history from db dumps.

South migration history is needed in db dumps so south knows the state
of the dump.
Convert emails in database dumps while preserving employee status.

Convert all @mozilla.com emails to XXXX@mozilla.com and all other
emails to XXXX@example.com so not all users are considered Mozilla
employees.
Merge pull request #1016 from glogiotatidis/dumpupdate

Update database anonymization script