Minor change to ArcanistInfrastructureTestCase::testLibraryMap

Summary: Modify ArcanistInfrastructureTestCase::testLibraryMap to use phutil_get_current_library_name() instead of hard-coding the library name.

Test Plan: See D9844.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9846