Add fedora-modular-beta.conf for f27
    
    Updated config options:
    * createrepo_deltas
    * media_checksum_base_filename
    * image_name_format
    * global_release
    * runroot_tag
    * global_target
    
    + Added comps (https://pagure.io/pungi-fedora/pull-request/407)
    
    Related issue:
    * https://pagure.io/releng/issue/7074
    
    Signed-off-by: Tomas Mlcoch <tmlcoch@redhat.com>