Fix git "origin" remote in more circumstances

Summary:
Fixes T4041. We currently detect when "origin" is incorrect, but can do better:

  - When "origin" is missing, we can add it. This happens for Git 1.7.1 -- see T4041.
  - When "origin" is wrong, we can fix it automatically if we control the repository.

We only need to fail when origin exists, is wrong, and we aren't in charge of the repository.

Test Plan: Ran `bin/repository discover X` on a repository with a good origin, no origin, a bad-but-under-control origin, and a bad-out-of-control origin. Got the right behavior in all cases.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran, champo

Maniphest Tasks: T4041

Differential Revision: https://secure.phabricator.com/D7614