Add phantomjs2 images
We want to keep the old images so the current stable and patch releases continue to pass tests using the previous phantomjs.
To help with https://gitlab.com/gitlab-org/gitlab-ce/issues/4216 and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5740
Currently this uses the official download location, which has bitbucket access throttling issues. We should open a repo in the gitlab-org group to mirror the packages we need.
An alternative approach here instead of creating more images, would be to have both images of phantomjs available, and let gitlab symlink the /usr/bin/phantomjs to the one it wants.