gitlab-ci-multi-runner and Docker executor: "git" may not be available

Hi,

Doc and code say:

The runner runs the line below before it runs the commands in your build script:

    cd /gitlab-ci-runner/tmp/builds && git clone git@gitlab_server_fqdn:group/project.git project-1 && cd project-1 && git checkout master

So gitlab-ci-multi-runner assumes git is available in the build environment and we are thus unable to use Docker images which are not including the git binary, that is to say most of them.

The workaround is of course to only use Docker images including git, but if the git binary could be "injected" in the runner when not detected, we could really use any images of the hub, given that once our .gitlab-ci.yml is executed, we can then manage dependencies on our own.

Let me know if I'm missing something here!

Thanks,