Fix purge of unwanted kernels on DNF based machines

[traylenator]

Pull Request (PR) description

Previously when installonly_limit of a node is adjusted then package-cleanup was called to remove unwanted old kernels. This is invalid for dnf based systems and a new command must be used.

This DNF command will remove kernel packages except in two cases:

• It is the running kernel as determined from $facts['kernelrelease']
• It is one of last N kernel versions where N is the installonly_limit

This Pull Request (PR) fixes the following issues

Fixes #295

[traylenator]

rebase after #308 for fedora test.