When repairing Git remote URIs, include credentials

Summary: See IRC. Currently, if a fetch fails, we may repair the remote URI incorrectly, replacing it with one without any credentials. Instead, retain credentials.

Test Plan: Faked it locally, got le-boom to verify on IRC.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D8055