Configure SSH key pairs For QA CI Runners

As part of gitlab-org/gitlab-qa#112 (closed) we needed to make the gitlab instances under test internet accessible. In collaboration with infrastructure we decided on SSH tunneling in https://gitlab.com/gitlab-com/infrastructure/issues/4298 to make them internet accessible.

Therefore in order to authenticate with the machine they will be SSH'ing into they will need an SSH key pair. Please ensure (somehow) that the runners that build gitlab-qa have SSH key pairs on them and please post their public keys on this issue so that we can ensure they have access to the tunnel VM.