LU-2912 mdd: move fid2path from MDD to MDT

LU-2912 mdd: move fid2path from MDD to MDT

1. Move some linkEA API to obdclass, so both MDD(set linkea)
and MDT(fid2path) can access these LINKEA operation.

2. Move fid2path from MDD to MDT, so it can detect remote
object, and return -EREMOTE to the client. Then the client
will try fid2path on another MDT, and finally the client
will assemble the path fragments from different MDT.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I464cd1fdd44ebbe02c94821f910294829f3d9b94
Reviewed-on: http://review.whamcloud.com/5676
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>