LU-3546 mdt: reply error to client after version check

This is missing from MDT implementation which will cause the client
to wait for reply forever.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I9e46d83f8db6b6ded57a284914a2ede88dd987f4
Reviewed-on: http://review.whamcloud.com/6864
Tested-by: Hudson
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>