Board manager: add link ID to show board inputs and outputs commands

Added the link ID to the table generated by the board-manager show board-inputs/outputs commands in order to make it easier to debug link tests.

Fixes #25 (closed).

Also added the docker tag to gitlab-ci.yml to force CI to use the old Gitlab runners as described here https://cern.service-now.com/service-portal?id=outage&n=OTG0078219.