LU-10419 lfsck: skip dead target

LU-10419 lfsck: skip dead target

Do not send LFSCK RPC to dead targets to avoid being blocked.
The patch adds warning message when try to send LFSCK RPC on
the non-full connection, it is helpful to understand why the
LFSCK may be blocked.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I0599eb961f1aabd58d0de53fd51f25ca1ec8ff34
Reviewed-on: https://review.whamcloud.com/31475
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>