LU-1445 ofd: remove ofd_seq_count and add ocd_seq

LU-1445 ofd: remove ofd_seq_count and add ocd_seq

Remove ofd_seq_count from the disk, so ofd_seq will
not be initialized during setup,  only be created during
connection or reconnection.

Change-Id: I6dad9aa960897f46afb0a5ea96d8330a227f36e4
Signed-off-by: Wang Di <di.wang@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/4325
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>