Use rake to start the test suite in Jenkins

Originally created by @bertagaz on #12503 (Redmine)

While we worked on the vagrant build switch part of tails#5630 (closed) (#11972 (closed) and friends), the Rakefile got improved with some code that can be used to start the test suite through rake test.

There’s been a pull request to use switch to this in Jenkins.

Related issues

Related to #11972 (closed)

Edited May 15, 2020 by bertagaz

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