add Fedora 21 template

For Fedora 21, the kickstart has been updated to work better on
physical hardware.  In general, I’ve simplified things and removed bits
I had previously cargo-culted from other sources but later found to be
unnecessary.

This commit also starts a directory structure refactor that will couple
the provisioning scripts with distro releases.

NOTE: The Fedora 19 templates will be removed from this repo after
official support ends on January 6, 2015.