CBQE-0 print out what server failed to download binary

Change-Id: I5e1c39eb18734c49a0d6576a4c2b87213112827e
Reviewed-on: http://review.couchbase.org/42860
Reviewed-by: Thuan Nguyen <soccon@gmail.com>
Tested-by: Thuan Nguyen <soccon@gmail.com>