Improve Fedora support for nova element

- on systemd based distros create a .service file for dnsmasq
- check and create the libvirtd group if it doesn't already exist
- handle distro-specific location for the pxelinux.0 file

Change-Id: If24e061701c48df08342642199e765c61dca8a75
Merge "Improve Fedora support for nova element"