Make it easier to opt-out from the playground
    
    When 'fedpkg request-branch' requests for an 'epel8' (or higher),
    Fedora SCM will create also 'epel8-playground' branch and place
    initial commit containing 'package.cfg' into 'epel8'. This allows
    avoiding the creation of the extra 'epel8-playground' branch
    and the commit. New argument '--without-playground' was added.
    
    JIRA: RHELCMP-589
    Resolves: rhbz#1746314
    
    Signed-off-by: Ondrej Nosek <onosek@redhat.com>