Fix dep8 autopkgtests, make Salsa CI fully green

See commits for details.

Contribution is based on branch debian and targets branch debian based on comments in !21 (comment 648392)

There are extra commits as while I was developing this, the contents of debian branch was force pushed by the maintainers and it jumped from aad4831e to b9f2ea23 to 32e9a61f. Rebased on latest debian.

I am not a Perl expert and I probably need to remove some changes that turned out to be unnecessary before this is finalized, but this is good enough for feedback/review.