Check if yum is really present on a 'redhat' machine. Only if it is,
enable the Yum bucket. The same for DNF since older versions of CentOS
and Fedora do not ship DNF.
If the folder `/car/cache/dnf` is present, the content will be cached
like in the Yum plugin.
A possible configuration to enable it:
Vagrant.configure(2) do |config|
config.vm.box = "fedora/24-cloud-base"
if Vagrant.has_plugin?("vagrant-cachier")
config.cache.scope = :machine
config.cache.auto_detect = false
config.cache.enable :dnf
end
end
