Custom handler for koji watch_tasks
    
    Output text during rhpkg/fedpkg build process states that there
    is a 'watch_task' subcommand. When 'koji_cli' library is imported
    in rhpkg/fedpkg tool, it shows that command is named
    'rhpkg/fedpkg watch_task' instead of 'brew/koji watch_task'. Custom
    handler replaces the internal one inside koji_cli library.
    Additional fix in rhpkg is needed after this change is released.
    
    Relates: rhbz#1570921
    Relates: COMPOSE-2809
    
    Signed-off-by: Ondrej Nosek <onosek@redhat.com>