Encapsulate instance test scenarios inside a Docker image

As per #25 (closed) we need to extract instance test scenarios and encapsulate these inside a Docker image.

Docker image should expose an Entrypoint to make it possible to run instance test scenarios against GitLab instance.

Pass instance address as an argument, pass login and password as environment variables.

mentioned in issue #30 (closed)

mentioned in issue #32 (closed)

mentioned in issue #25 (closed)

changed title from Encapsulate instance test scenario inside a Docker image to Encapsulate instance test scenarios inside a Docker image

mentioned in merge request !54 (merged)

mentioned in merge request !57 (merged)

closed via merge request !57 (merged)

closed via commit 2518e7d1

changed milestone to %9.0