Fixes to mailman migration script

Fixed syntax errors, added an option to only remove, and not add users, and
bonus whitespace nitpicking.
More fixes to mailman migration

(cherry picked from commit cb292e99550c15c67566959ad2be9a5fb21e0290)
Add mailman error handling to mailman migration
Merge pull request #1507 from learning-unlimited/mailman-migration-fixes

Mailman migration fixes