General cleanup of the specfile
- python_sitelib was defined but never used
- _with_python3 was True, so I removed the ifs
- python3_pkgversion is defined on both Fedora and EPEL
- %{py3dir} is deprecated and not needed here
- use %pyX_build and %pyX_install macros, stop using %{__python}
- run tests against the installed version
- some cruft removal