Since the message confirming outgoing transfer completion is logged
asynchronously, it may happen that transfer statistics may not yet be
logged by the time the dig command triggering a given transfer returns.
This causes false positives for the "ixfr" and "xfer" system tests.
Prevent this from happening by checking outgoing transfer statistics up
to 10 times, in 1-second intervals.
(cherry picked from commit 9fc5e48b14)
8c1c47b22b