txcouchbase test_ops: Check res_fail rather than res
txcouchbase test_ops: Check res_fail rather than res

This somehow accidentally worked in previous runs, because often
res_fail is res

Change-Id: Ieb7da9871bec2494c38527eee1266d99e136a264
Reviewed-on: http://review.couchbase.org/37079
Tested-by: Mark Nunberg <e7d42768707bf23038325b0b68d4b577e5f6064a@haskalah.org>
Reviewed-by: Volker Mische <fb414f8ac0dbbf87663550ae4ef5fc95b1041941@gmail.com>

couchbase/couchbase-python-client,mnunberg/couchbase-python-client,couchbase/couchbase-python-client,mnunberg/couchbase-python-client