LU-11761 fld: let's caller to retry FLD_QUERY

LU-11761 fld: let's caller to retry FLD_QUERY

In fld_client_rpc(), if the FLD_QUERY request between MDTs fails
with -EWOUDBLOCK because the connection is lost, return -EAGAIN
to notify the caller to retry.

It also reverts the patch https://review.whamcloud.com/12586/, which
was landed on b2_6_90_0-5-g6db07f0 to avoid returning -EAGAIN from
lod_object_init() to confuse lu_object_find_at() (thinks the object
was dying when it encounters -EAGAIN). In current Lustre version,
lu_object_find_at() just returned found object and let's caller to
check whether it's dying.

Fixes: 6db07f095fba ("LU-5871 lod: Do not return EAGAIN in lod_object_init")

Lustre-change: https://review.whamcloud.com/34962
Lustre-commit: e3f6111dfd1c6f2266d0beef67e5a7514a6965d0

Change-Id: Ie83ebfdae2bd50c96a59a065f7f3c3dcfad04e42
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Lai Siyao <lai.siyao@whamcloud.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/35661
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Stephan Thiell <sthiell@stanford.edu>
Reviewed-by: Oleg Drokin <green@whamcloud.com>