fedora-common-ostree: Make presets canonical
    
    This ensures that only services defined in presets are enabled by
    default. This has two advantages:
    - services enabed in RPM scriptlets are dropped
    - new services can be enabled by default simply by adding them to
      presets
    
    This mirrors the behaviour of Fedora CoreOS. For more informations, see:
    - https://github.com/coreos/fedora-coreos-config/blob/testing-devel/manifests/ignition-and-ostree.yaml#L39..L48
    - https://github.com/coreos/fedora-coreos-config/pull/73
    - https://github.com/coreos/fedora-coreos-config/pull/77
    - https://github.com/coreos/fedora-coreos-config/pull/122
    - https://github.com/coreos/rpm-ostree/issues/1803