dev-util/debian-devscripts: fix broken tests

Some tests don't work properly. Some tests didn't work with libarchive tar and some require python. The python tests are disabled and a hard dependency on app-alternatives/tar[-libarchive] is added to enforce using a working tar implementation for tests.

Signed-off-by: Adrian 'nex' Schollmeyer adrian.schollmeyer@fem.tu-ilmenau.de