Fix user with missing current group migration

cc @brandondunne @Fryguy @lfu @dajohnso 

Thanks @Fryguy for helping pairing/reviewing on this one.

To address https://bugzilla.redhat.com/show_bug.cgi?id=1145794
Does this line conflict with https://github.com/jrafanie/manageiq/blob/fix_user_with_missing_current_group_migration/vmdb/app/models/miq_group.rb#L24?