LU-1445 osd: Add multiple sequence support for osd-zfs

LU-1445 osd: Add multiple sequence support for osd-zfs

Add osd_seq_list for osd-zfs, then it can allocate new sequence
after FID on OST is landed.

Test-Parameters: mdtfilesystemtype=zfs ostfilesystemtype=zfs
Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I66bae3987a1ae167aa48a3a1d4b6e50f300f1dd8
Reviewed-on: http://review.whamcloud.com/4837
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>