This also moves the packages to be installed into a file that can be
shared between test methods.
It drops several packages that are unnecessary for testing, and excludes
those paths from pylint checks using pocketlint.
Related: rhbz#1785154
Without this, depending on which version of pylint is used, you may see
errors related to the rpm.RPMTAG_* constants. This makes sure that
pylint allows loading the rpm module.
Related: rhbz#1785154
