Add bin/auth refresh for debugging OAuth token refresh issues

Summary: Ref T2852. Provide a script for inspecting/debugging OAuth token refresh.

Test Plan: Ran bin/auth refresh with various arguments, saw token refreshes.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2852

Differential Revision: https://secure.phabricator.com/D6276