staging/lustre/obdclass: use common way to store lastid

Local files last id are stored in root in files named seq-xxx-lastid
while lastid for OST objects is stored in O/seq/LAST_ID special
object with zero OID and handled by OSD.
Patch reworks local files lastid to be stored in O/seq/LAST_ID too
and using the same format.

Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-2886
Lustre-change: http://review.whamcloud.com/6199


Signed-off-by: Mikhail Pershin <mike.pershin@intel.com>
Signed-off-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>