LU-17658 fid: check on disk sequence before allocating to osp

LU-17658 fid: check on disk sequence before allocating to osp

If we lose the commit to update seq_srv on ofd/ost, the available
super-sequence range is not updated, the sequence server of ofd
could assign the same sequence again to a different osp,
creating filesystem corruption.

To address this, a new dt_device_operations->dt_last_seq_get()
is added to iterate the current known sequence dirs under /O
and return the latest one. Before using the super-sequence range
read from seq_srv we use the new interface to double check and
update the current range or get a new range if necessary.

Change-Id: I49a11bb3b5e476e55c5835b05392c9567aeeb4ce
Signed-off-by: Li Dongyang <dongyangli@ddn.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54474
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Qian Yingjin <qian@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>