[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 <email@example.com>