Add koji as BuildRequires
    
    koji.read_config() now throws error if config search
    path is empty. See https://pagure.io/koji/pull-request/1787
    
    Fixes: RHBZ#1799575
    
    Thanks to Dodji for figuring out the root cause of build failure
    
    Signed-off-by: Sinny Kumari <sinny@redhat.com>