Update migrateUserGroup to deal with primary key issue

Update migrateUserGroup to deal with primary key issue

Update migrateUserGroup so that if a user is in both the old group and
the new group, the script still succeeds.  Otherwise, it will fail
with violations to the PRIMARY KEY index on the user_groups table.

Change-Id: I7bfda03f5735633d03b81092dad29d73293cd182