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
This test case is for a user who has both current_group and miq_groups set, but current_group is not in miq_groups.