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#8667 (closed):

• 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: #5288 (closed)

Related issues

• Blocked by #6564 (closed)
• Blocked by tails#8667 (closed)