CBQE-1350: Store HTTP status code as property

Store the returned HTTP status code in a property and don't add
it to the error message. There's currently code that checks for
the error message that would break. Having a separate property
is the cleaner approach anyway.

Change-Id: If1d700c8cf81f58df03bf8b8269a64d481b43031
Reviewed-on: http://review.couchbase.org/38176
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>