Use alternative way to check SSH host key

In the ssh keys section (https://docs.gitlab.com/ee/ci/ssh_keys/README.html), an alternative to overwriting the ssh config *(echo -e "Host \n\tStrictHostKeyChecking no\n\n" > ~/.ssh/config') is to use ssh-keyscan:

$ mkdir -p ~/.ssh
$ ssh-keyscan -H hostname.com >> ~/.ssh/known_hosts