Include the unit status in the getdiff conduit method

Summary:
We need to query the unit status in order to determine if
there are postponed unit tests to update after running "arc unit"

Test Plan:

1. set my conduit uri to a server running the new code
2. ensured unitStatus existed when retrieving a diff

Reviewers: epriestley

Reviewed By: epriestley

CC: dpepper, aran, epriestley

Differential Revision: 918