pungi-koji: Allow user to specify version component count in latest symlink
    
    This change adds an option which allows users to specify
    the number of version components (i.e. values between dots)
    
    The default behavior is preserved, and is equivalent to using
    '-1' as the value.
    
    - Negative values remove items from the end.
    - Positive values specify the count of of components
    - Zero will remove the version field entirely from the symlink
    - When nonzero, at least one version component will appear
    
    Merges: https://pagure.io/pungi/pull-request/1361
    Signed-off-by: Lon Hohberger <lhh@redhat.com>