Make test commit work with repositories specified with `git`

[andreeaflorescu]

test_commit_format forever hangs when the repository is specified with git instead of https.
The reason it hangs is that doing git fetch in the docker container awaits user input to fetch from the unknown host (in this case github). A quick fix here is to run ssh-keyscan -t rsa github.com >> ~/.ssh/known_hosts before calling git fetch. This way at least the test will just fail, and not hang.

The second problem is that we need to forward the ssh keys on the host for git to work (and configure the ssh agent). No idea how to do that in a safe/sane way.