ceph_objectstore_tool: When exporting to stdout, don't cout messages

Fixes: #10128
Caused by a2bd2aa7

Signed-off-by: David Zafman <dzafman@redhat.com>
(cherry picked from commit 0d5262ac2f69ed3996af76a72894b1722a27b37d)
Merge pull request #2958 from ceph/wip-10128-giant

ceph_objectstore_tool: When exporting to stdout, don't cout messages

Reviewed-by: Loic Dachary <ldachary@redhat.com>