Run the test suite automatically on Git push

Originally created by @intrigeri on #6565 (Redmine)

Once we have a platform to run the automated test suite, we can plug it into our Jenkins setup to run it automatically on autobuild ISO images.

Based on the results of tails/tails#8667:

write library code that implements the (successful Jenkins ISO build job -> if/what needs to be tested) mapping;
research and quickly try out the various options available to implement the specified needs with Jenkins; the deliverable is a blueprint comparing these options, proposing a design, and finally leading the discussion towards a decision;
implement the chosen design.

Zuul might be useful for this.

Parent Task: tails/sysadmin#5288

Edited May 15, 2020 by intrigeri