feat(libvirt): Rework documentation around using config drive.
feat(libvirt): Rework documentation around using config drive.

iankronquist/docs,michelleN/docs,wli6/docs,marineam/coreos-docs,jonboulle/docs,jdloft/docs,coreos/docs,skynet/docs,ksmaheshkumar/docs-2,joshix/docs,mischief/coreos-docs,hkjn/docs-1,ionave/docs,atxwebs/docs,robszumski/docs,mjg59/docs,endocode/coreos-docs,bq-xiao/docs