Encapsulate OS differences in params class

thus adding support for Debian/Ubuntu.
By default, we assume sensible names (those of rhel)..
This is also so we pass rake spec tests
correctly test for libvirt being installed & running

missed on place where libvirtd was referenced directly as service,
that's fixed now. Also, after initial doubt I have now verified that
yes, you can indeed run libvirt in virtualbox, so we can actually test
for this!
document debuntu support & :shipit:
Merge pull request #5 from igalic/debian-support

Add Debian support