ServiceCache::getInstances do not return any instances

we've run into an issue with service discovery after upgrading from 4.3.0 to 5.6.0.

ServiceCache::getInstances do not return any instances of a service. restarting the back-end services do allow ServiceCache to detect the instance. have managed to simulate this scenario in the test cases.

TestServiceCache::testInitialLoad was modified to register instance1 before the cache has been started. an assert immediately after cache.start detects the failure, ie:

assertEquals(1, cache.getInstances().size());