Support overriding Zookeeper connector to production via env property

This will allow to run production connector (and no stub runner) without `prod` profile (e.g. under `dev`) if `microservice.production` is defined
please make those private static final TESTING_CONDITION (the same applies to other conditions presented below)

if you don't add private or public or any other modifier then in fact you're creating a static property - in other words with this code a public static getter is added (which makes no sens of course)