spec/proxy: fix tests that expect wrong key in the cache
spec/proxy: fix tests that expect wrong key in the cache

These tests were passing just because proxy:authorize was being called
with the wrong arguments. We were sending a table with usages, but in
reality, this method expects a string with the usage formatted.

3scale/apicast,3scale/apicast,3scale/apicast,3scale/apicast,3scale/docker-gateway,3scale/docker-gateway