LU-1757 brw: Fix short i/o and enable for mdc

LU-1757 brw: Fix short i/o and enable for mdc

The short i/o flag was left out of the OST flags in the
original patch, meaning it was not really on.  Also, the
short_io_size value was used uninitialized, meaning it
was sometimes non-zero, which coudl lead to several issues.

Also add the short i/o flag to the MDC/MDT for data on MDT.
Quick testing suggests this works fine with no further
changes.

Cray-bug-id: LUS-187
Signed-off-by: Patrick Farrell <paf@cray.com>
Change-Id: I4154b87d5ad73b53467b0382368fad7c5ba177fe
Reviewed-on: https://review.whamcloud.com/30435
Tested-by: Jenkins
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>