Improve EndpointController dual-stack testing

Rewrite some of the test helpers to better support single-stack IPv4
vs single-stack IPv6 vs dual-stack IPv4 primary vs dual-stack IPv6
primary, and update TestPodToEndpointAddressForService to test some
more cases.

Author: danwinship

pkg/controller/endpoint/BUILD

@@ -64,6 +64,7 @@ go_test(
         "//staging/src/k8s.io/client-go/tools/cache:go_default_library",
         "//staging/src/k8s.io/client-go/util/testing:go_default_library",
         "//staging/src/k8s.io/component-base/featuregate/testing:go_default_library",
+        "//vendor/k8s.io/utils/net:go_default_library",
         "//vendor/k8s.io/utils/pointer:go_default_library",
     ],
 )