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
Fix up 2to3 complaints. I've decided to do with wrapping list
comprehension inside list() to get the generators to run in several
places instead of list(map( or list(filter( which seem less readable to
me.
