Discovery service can't notify gateway about instance registration changes

[CarsonCook]

Logs show in the following form:

discovery-service_1    | 2021-01-14 19:32:53.758 <ZWEADS1:ThreadPoolTaskExecutor-1:1> root ERROR (o.z.a.d.GatewayNotifier) ZWEAD400E Cannot notify Gateway on 'https://gateway-service:10017/gateway/cache/services/apicatalog' about new instance 'api-catalog-service:apicatalog:10014'

The discovery service can't notify the Gateway or API Catalog about instances going down, or new instances registered. This will block dynamic API registration, as well as the API Catalog showing services as up when they are actually down.

This is likely due to the host name issue also documented in #9.