LU-911 obdclass: la_from_obdo helper

LU-911 obdclass: la_from_obdo helper

- OFD will need la_from_obdo() conversion.
- Fix obdo_from_la() to work with la flags.
- Call obdo_set_parent_fid() directly when needed instead of
  using obdo_from_inode() just to update parent fid
- Make obdo_from_inode() consistent with its name and don't
  update parent FID from.

Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Change-Id: Ib1a7d0a4a3e19434ae48c74b06b153d2fc5e5d78
Signed-off-by: Mikhail Pershin <tappro@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1848
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>