cephfs-journal-tool: get and check layout info during dump/undump

cephfs-journal-tool: get and check layout info during dump/undump

when cephfs-journal-tool import journal, it uses default layout
to get object_size, this is wrong. Because default objetct_size
can be changed by Config option change mds_log_segment_size when
cluster initialized.

The fix is save the layout info to header during journal export,
When improt journal, first try to get layout from cluster, if failed,
then get layout info from dumped journal file, if still failed, set
layout to default.

Fixes: http://tracker.ceph.com/issues/24644
Signed-off-by: Gu Zhongyan <guzhongyan@360.cn>
Signed-off-by: yupeng chen chenyupeng-it@360.cn