common: rpm-ostree variant support

[JGoutin]

Add support for rpm-ostree Fedora variants.

Required changes:

• Everything related to DNF or using DNF.
• GRUB2 Kernel options requires:

  # List options
  rpm-ostree kargs
  # Add Options
  rpm-ostree kargs --append audit=1 --append audit_backlog_limit=8192 --append vsyscall=none --append pti=on --append slub_debug=P --append page_poison=1 --append page_alloc.shuffle=1 --append efi=disable_early_pci_dma --append iommu.strict=1 --append amd_iommu=on --append init_on_free=1 --append init_on_alloc=1 --append debugfs=off

Only on "common" for now, servers software is intended to be installed using containers on ostree variants. But, "common" role can be used to bootstrap any machine.