Ignoring flush errors makes it possible for callers to never know that
their writes didn't succeed, and allows writes to be lost if the pool
fails.
This commit gives zio_flush() a flag argument, and updates the call
sites to pass ZIO_FLAG_DONT_PROPAGATE to it. Thus, this commit does not
change any behaviour, but opens the floor for further changes to allow
those callers to handle flush failures sensibly.
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
(cherry picked from commit 6d0deb8a5a0c3d6bbc69d9625d55fc776bb98ea3)
8ec175d7e1