LU-10985 mdt: properly handle unknown intent requests

LU-10985 mdt: properly handle unknown intent requests

Invalid intent requests should be rejected early on,
so the later code does not make any assumptions about
validity of various structures like extended pills
and such.

Change-Id: I74de899ae6cea7017ae8ca9a8c488ca801a38c5d
Signed-off-by: Oleg Drokin <oleg.drokin@intel.com>
Reviewed-on: https://review.whamcloud.com/32237
Tested-by: Jenkins
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>