GitLab

See merge request !5

scripts/gitlab-runner-helper sets umask to 0000 to fix issues where ci
jobs would be running as a different user, preventing access to files.

This causes issues when files in repositories end up in build artifacts
with world writable permissions.

One such example is the alpine-gitlab-ci project where `/etc/sudoers.d`
ends up word-writable, preventing sudo to work.

Set it to the standard 0022 to fix this issue.

See merge request !4

dockerfile: install gitlab-runner-helper from community

See merge request !3

ci: upload images to docker

See merge request !2

add Dockerfile to build an image

See merge request !1