Go 1.9 update

change to use go 1.9.x use alpine and multistage build to bring image size down to ~15MB rather than ~600MB. removed gitlab.com/gitlab-org/gitlab-ci-multi-runner/helpers to use just github.com/fsouza/go-dockerclient - this was needed in order to force remove images. set default values to production levels

This is really important. Can someone in the Gitlab team take a look at this and !3?