LU-1187 osd: allocate osd_compat_objid_seq dynamically

LU-1187 osd: allocate osd_compat_objid_seq dynamically

1. Allocate osd_compat_objid_seq dynamically, so osd can load
as many as seq it wants.
2. Change group to seq.
3. remove the compat from name, because we will still use
the same disk-layout for FID on OST.

Change-Id: I52d40ecd805aa44074838496e44ed2b71fd39f92
Signed-off-by: Wang Di <di.wang@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/4323
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>