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

Fixes: #10128
Caused by a2bd2aa7

Signed-off-by: David Zafman <dzafman@redhat.com>
ceph_objectstore_tool: Make --file option consistent by treating "-" as stdout/stdin

Signed-off-by: David Zafman <dzafman@redhat.com>
tests: ceph_objectstore_tool.py test all variants of export/import

Handle change of error message text

Signed-off-by: David Zafman <dzafman@redhat.com>
Merge pull request #2950 from ceph/wip-10128

Wip 10128

Reviewed-by: Loic Dachary <ldachary@redhat.com>