Use correct route to prefill hawkular hostname

Plural `get_routes` ignores `:name`, was querying /oapi/v1/routes and
returning all routes in all namespaces, and we were picking a random one.

`get_route` queries
/oapi/v1/namespaces/openshift-infra/routes/hawkular-metrics
giving the right route or nil.

app/controllers/mixins/ems_common_angular.rb

@@ -434,7 +434,7 @@ def set_ems_record_vars(ems, mode = nil)
 
     def get_hostname_from_routes(ems, hostname, port, token)
       client = ems.class.raw_connect(hostname, port, :bearer => token)
-      client.get_routes(:name=>'hawkular-metrics').first.try(:spec).try(:host)
+      client.get_route('hawkular-metrics', 'openshift-infra').try(:spec).try(:host)
     end
 
     def build_connection(ems, endpoints, mode)