LU-2733 osd: osd-zfs to initialize existing sequence

osd_find_or_add_seq() to use osd_oi_find_or_create() so that
existing sequence is loaded if exists

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: I9f173615ef047dd4696d8ed51687c7c268b32dbf
Reviewed-on: http://review.whamcloud.com/5247
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>