import-spec: script for importing upstream spec
    
    The canonical spec file is now upstream since:
    https://github.com/projectatomic/rpm-ostree/pull/1900
    
    Add a script to make it trivial to import the spec file here and merge
    the changelog. There's a `--keep-v-r` flag one can use to keep the
    Version and Release tags of the existing spec file to deal with e.g. git
    snapshots (though ideally continuous builds will eventually be handled
    automatically).