Due to possible performance problems when DiscoveryClient gives nonexistent DNS name as local address Local endpoint is created from server properties by default.

Local Ip determined from spring.commons InetUtils.
    To enable local endpoint resolution via service discovery, DiscoveryClient must be present and 'spring.zipkin.service.locator.discovery' should be set to true.
    FallbackHavingEndpointLocator was caching and recreating EndpointLocator in the same time - removed the caching part.

    Fixes gh-403

docs/src/main/asciidoc/spring-cloud-sleuth.adoc

@@ -298,6 +298,21 @@ By default Sleuth assumes that when you send a span to Zipkin, you want the span
 spring.zipkin.service.name: foo
 ----
 
+=== Host locator
+
+In order to define the host that is corresponding to a particular span we need to resolve the host name
+and port. The default approach is to take it from server properties. If those for some reason are not set
+then we're trying to retrieve the host name from the network interfaces.
+
+If you have the discovery client enabled and prefer to retrieve the host address from the registered
+instance in a service registry then you have to set the property (it's applicable for both HTTP and
+Stream based span reporting).
+
+[source,yaml]
+----
+spring.zipkin.locator.discovery.enabled: true
+----
+
 == Span Data as Messages
 
 You can accumulate and send span data over