Add support for dnf
Created by: schvabodka-man
Hello. Currently yum is getting obsolete in RHEL/Fedora/CentOS and it's being replaced by the dnf. The cdist still doesn't have "native" support for dnf, only __package_yum and this makes cdist hard to use on new fedora/centos versions. Would be really awesome if there would be __package_dnf