Summary:
There was a recent change in mercurial and revsets
shouldn't return lists anymore. This diff fixes it.
This diff also fixes git diff handling. It returned not even a list,
but a single rev number. Unfortunately it's not tested because we need to
mock conduit response.
Test Plan: arc unit
Reviewers: #mercurial, ikostia
Reviewed By: ikostia
Subscribers: ikostia, kulshrax, mjpieters, #sourcecontrol
Differential Revision: https://phabricator.intern.facebook.com/D4938930
Signature: t1:4938930:1493051696:cfb278773e5932d5f38942b0a0ca49f018ec5083
