Support for synchronous calls

At the moment the only option possible to automate the re-deployment of a configuration on OpenShift gateway is to reduce the configuration cache to the very minimum (60 s). For some customers and some specific situations (need for a stricter rate limit check and very low network latency) it would be preferable to have the option of selecting synchronous calls in APICAST configuration. This would translate in having 0 (zero) TTL for configuration cache.