DNF is the package manager used on Fedora systems and will also most
likely replace yum for the next generation of RHEL. Along with the
implementation here an example JeOS image description for Fedora can
be found on: https://github.com/SUSE/kiwi-descriptions.
This Fixes#36
nose is no longer maintained, thus we have to move to another
testing system. This commit updates the tox setup and all tests
to use pytest instead of nose.
