LU-1303 fld: verify support for range lookups

LU-1303 fld: verify support for range lookups

if the underlying storage does not support range lookups,
then FLD disables any mappings with server index different
from 0, thus disabling DNE and FID-on-OST features.

Signed-off-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Change-Id: Id93b01385acfafde024dff33557656afdcd1e4b3
Reviewed-on: http://review.whamcloud.com/4133
Reviewed-by: Mike Pershin <tappro@whamcloud.com>
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>