ui: Ensure routing tab is shown when connect enabled (#8209)

In https://github.com/hashicorp/consul/pull/8065 we attempted to reduce
the amount of times that the UI requests the discovery chain endpoint
when connect is disabled on a datacenter.

Currently we can only tell if connect is disabled on a datacenter by
detecting a 500 error from a connect related endpoint.

In the above PR we mistakenly returned from a catch instead of
rethrowing the error, which meant that when a none 500 error was caught
the discovery chain data would be removed. Whilst at first glance this
doens't seem like a big problem due to the endpoint erroring, but we
also receive a 0 error when we abort endpoints during blocking queries.
This means that in certain cases we can remove cached data for the
discovery chain and then delay reloading it via a blocking query.

This PR replaces the return with a throw, which means that everything is
dealt with correctly via the blocking query error detection/logic.

ui-v2/app/services/repository/discovery-chain.js

@@ -24,7 +24,7 @@ export default RepositoryService.extend({
           }
           return;
         default:
-          return;
+          throw e;
       }
     });
   },