LU-1445 mdt: allow lightweight connection even if no OST

LU-1445 mdt: allow lightweight connection even if no OST

MDT should allow lightweight connection from OST even if there
is no OST being activated, because OST might need do FLD lookup
during recovery phase.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: Ica44aafdbcbf29f10d314bc65de8c1f5ff5d2940
Reviewed-on: http://review.whamcloud.com/4920
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <alexey.zhuravlev@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>