LU-7848 target: Do not fail MDT-MDT connection

LU-7848 target: Do not fail MDT-MDT connection

When one MDT restarts, and try to connect to another
MDT with the new cookie, let's do not fail it, otherwise
it might cause eviction between MDT.

Signed-off-by: Di Wang <di.wang@intel.com>
Change-Id: I3d2e0712ee0ed05bdf46c7781e190206a6dcfb1c
Reviewed-on: http://review.whamcloud.com/18800
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>