Move most code in Role::Reader to PP

There's very little actually shared between PP and XS
Not using tempdir in this test
Small formatting tweak
Improve test descriptions
Move _ipv4_start_node to PP class
Fixed type import confusion
Explicitly mark tests which are only for the pure Perl code

This is for the benefit of a script in the XS repo that will copy the tests
from the PP repo.
Merge branch 'dave/refactor-roles'