Fix LDAP group sync regression for groups with member value `uid=<username>`

Drew Blessingrequested to merge
dblessing/gitlab:regression-ldap-group-synchronization-is-broken-for-our-company-s-ldap-with-gitlab-8-6-442 into master

Closes #442 (closed)

A simple (if not elegant) way to resolve this issue. AND there are tests so this won't happen again.

Merge request reports