Add common/djangoapps/third_party_auth; update pylintrc to allow test_* names.

third_party_auth contains a working settings mechanism, the start of the provider interface + 3 implementations (Google, Mozilla Persona, LinkedIn), and a stub for the auth pipeline. Modified existing lms settings files to use but deactivate the module.
Merge pull request #2736 from johncox-google/johncox/feature/auth

Add auth module