test: remove old module_blacklist setting

This is now inherited via the namespace walker classes from
snakeoil.test.mixins.
travis-ci: use coverage instead of pytest-cov

I've had various troubles making pytest-cov generate proper coverage
data in certain cases and this allows us to more easily use an
alternative to pytest if we want to.
move chksum tests out of submodule

Using a flat test submodule makes things simpler, especially if we ever
want to externalize the unit tests from the core module in the future.
setup: simplify various metadata settings
default to module.test for the test namespace

This way we can remove the nearly worthless test class overrides from
the various pkgcore projects setup.py files.