Fix an issue with setting "Real Name Attributes" in LDAP auth

Summary: We currently don't read/save this value correctly. Fix the issue. Ref T1536.

Test Plan: Set real name attributes to "x, y".

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, colegleason

Maniphest Tasks: T1536

Differential Revision: https://secure.phabricator.com/D6388