[koji-wrapper] Retry watching on connection errors
    
    With this patch Pungi should be more tolerant of network failures when
    running a blocking command (creating live media or live images).
    
    If the connection drops and the output indicates network problems, Pungi
    will try to watch the task with `koji watch-task`. This will be retried
    until it finishes (successfully or with some other failure). There is an
    increasing timeout after each retry. Currently the maximum number of
    retries is not limited.
    
    Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>