LU-1445 osd: add fld look up in osd.

Lookup FLDB during oi_insert, so we know it is MDT or
OST objects. And it also needs to init FLD service
on OFD as well, so object on OST can lookup FLDB
as well.

Change fci_lock to read/write lock, since fld_cache_lookup
will become the hot path after FLD lookup is added in OSD
layer.

Change-Id: I79ef723de603214b7136a51c36f0cb63513b5640
Signed-off-by: Wang Di <di.wang@intel.com>
Reviewed-on: http://review.whamcloud.com/4330
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>