test/rgw/notifications: prevent client retries to avoid duplicates

test/rgw/notifications: prevent client retries to avoid duplicates

if the RGW is slow, and the client retry, it may cause test to fail
since the number of notifications would be off.
in addition, in slow RGW, we need to verify that the expiry time did
not pass before checking the queue, so we see the expected number of
entries in the queue before they expire.

Fixes: https://tracker.ceph.com/issues/70756
Signed-off-by: Yuval Lifshitz <ylifshit@ibm.com>