test/neorados: Catch timeouts in Poll test

test/neorados: Catch timeouts in Poll test

The test is fragile against timing issues which manifest from time to
time on Teuthology. Catch the exception and print an error so it's not
hidden completely, but stop signaling it as a test failure.

I can do something more later, for now just stop having it bother the
RADOS team.

Fixes: https://tracker.ceph.com/issues/70916
(This time for real!)

Signed-off-by: Adam C. Emerson <aemerson@redhat.com>