This is because the meson build requires meson 0.47, which is not
available in the current Ubuntu LTS (18.04).
Signed-off-by: Arnaud Rebillout <arnaud.rebillout@collabora.com>
This adds a Dockerfile to generate a Docker image with the required
dependencies on top of the standard Ubuntu 18.04 image. The Gitlab CI
then runs the PulseAudio build within this image.