Ensure that e2e tests run on gce|gke and are appropriately

skipped for other cloud providers.

test/e2e/service.go

@@ -47,7 +47,7 @@ var _ = Describe("Services", func() {
 	})
 
 	It("should provide DNS for the cluster", func() {
-		if testContext.Provider == "vagrant" {
+		if providerIs("vagrant") {
 			By("Skipping test which is broken for vagrant (See https://github.com/GoogleCloudPlatform/kubernetes/issues/3580)")
 			return
 		}