In this CI test, we add the upstrem postmarketOS/pmaports.git
remote to the checked out git repository. Do not crash when it exists
already, so we don't need to remove it before each run when testing
locally.
* Move a comment that was after a line of code above that line. That
line was very long compared to all others in the file, and now the
file fits in 80 characters in every line, like PEP-8 recommends.
* Replace "folder" with "dir" in the comments (as I learned lately
that "folder" is only a Windows concept).
Copy all test cases from the pmbootstrap repository, that are actually
testing the aports. They were all adjusted to work nicely in this
repository, together with a brand new set of gitlab-ci configs.
This also includes the changes from this merge request, that had a
better detection of changed packages:
<https://gitlab.com/postmarketOS/pmbootstrap/merge_requests/1621>
