R1:c70f4815a958

Allow cluster devices to SSH to one another without acting as a user

Summary:
Ref T4292. When you run `git fetch` and connect to, say, `repo001.west.company.com`, we'll look at the current version of the repository in other nodes in the cluster.

If `repo002.east.company.com` has a newer version of the repository, we'll fetch that version first, then respond to your request.

To do this, we need to run `git fetch repo002.east.company.com ...` and have that connect to the other host and be able to fetch…