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