Use knative/pkg/test components for common things (knative#1937)

* Use knative/pkg components

* Update stringmatch method call as it has moved to common/v1alpha1 with istio

* Run update-deps after merge

* Fix nits

* Update docker repo variable to point to correct e2e repo

* Add a default serving namespace

Author: srinivashegde86

Gopkg.lock

@@ -36,8 +36,8 @@ required = [
 
 [[constraint]]
   name = "github.com/knative/pkg"
-  # HEAD as of 2018-08-23
-  revision = "3ca427071dcd0b1155830a19bce769b4902fa645"
+  # HEAD as of 2018-08-24
+  revision = "6eff182b8784a136e0ce20e47c5efbfe40ae6059"
 
 [[constraint]]
   name = "github.com/google/go-containerregistry"

Gopkg.toml

@@ -42,7 +42,7 @@ By importing `github.com/knative/serving/test` you get access to a global variab
 `test.Flags` which holds the values of [the command line flags](/test/README.md#flags).
 
 ```go
-imagePath := strings.Join([]string{test.Flags.DockerRepo, image}, "/"))
+imagePath := strings.Join([]string{test.ServingFlags.DockerRepo, image}, "/"))
 ```
 
 _See [e2e_flags.go](./e2e_flags.go)._
@@ -162,13 +162,13 @@ ready to serve requests right away. To poll a deployed endpoint and wait for it
 in the state you want it to be in (or timeout) use `WaitForEndpointState`:
 
 ```go
-err = test.WaitForEndpointState(
-		clients.KubeClient,
-		logger,
-		test.ServingFlags.ResolvableDomain,
-		updatedRoute.Status.Domain,
-		test.EventuallyMatchesBody(expectedText),
-		"SomeDescription")
+err = pkgTest.WaitForEndpointState(
+        clients.KubeClient,
+        logger,
+        updatedRoute.Status.Domain,
+        pkgTest.EventuallyMatchesBody(expectedText),
+        "SomeDescription",
+        test.ServingFlags.ResolvableDomain)
 if err != nil {
     t.Fatalf("The endpoint for Route %s at domain %s didn't serve the expected text \"%s\": %v", routeName, updatedRoute.Status.Domain, expectedText, err)
 }
@@ -185,7 +185,7 @@ service, you can directly use the `SpoofingClient` that `WaitForEndpointState` w
 
 ```go
 // Error handling elided for brevity, but you know better.
-client, err := spoof.New(clients.KubeClient.Kube, logger, route.Status.Domain, test.Flags.ResolvableDomain)
+client, err := pkgTest.NewSpoofingClient(clients.KubeClient.Kube, logger, route.Status.Domain, test.ServingFlags.ResolvableDomain)
 req, err := http.NewRequest(http.MethodGet, fmt.Sprintf("http://%s", route.Status.Domain), nil)
 
 // Single request.