Move testutil package to top-level

Since the common package no longer exists, the testutil package is being moved
up to the root. Ideally, we don't have large omnibus packages, like testutil,
but we can fix that in another refactoring round.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

api_test.go

@@ -14,11 +14,11 @@ import (
 	"testing"
 
 	"github.com/docker/distribution/api/v2"
-	"github.com/docker/distribution/common/testutil"
 	"github.com/docker/distribution/configuration"
 	"github.com/docker/distribution/digest"
 	"github.com/docker/distribution/manifest"
 	_ "github.com/docker/distribution/storagedriver/inmemory"
+	"github.com/docker/distribution/testutil"
 	"github.com/docker/libtrust"
 	"github.com/gorilla/handlers"
 )

client/client_test.go

@@ -9,9 +9,9 @@ import (
 	"sync"
 	"testing"
 
-	"github.com/docker/distribution/common/testutil"
 	"github.com/docker/distribution/digest"
 	"github.com/docker/distribution/manifest"
+	"github.com/docker/distribution/testutil"
 )
 
 type testBlob struct {

digest/verifiers_test.go

@@ -7,7 +7,7 @@ import (
 	"os"
 	"testing"
 
-	"github.com/docker/distribution/common/testutil"
+	"github.com/docker/distribution/testutil"
 )
 
 func TestDigestVerifier(t *testing.T) {

storage/layer_test.go

@@ -9,10 +9,10 @@ import (
 	"os"
 	"testing"
 
-	"github.com/docker/distribution/common/testutil"
 	"github.com/docker/distribution/digest"
 	"github.com/docker/distribution/storagedriver"
 	"github.com/docker/distribution/storagedriver/inmemory"
+	"github.com/docker/distribution/testutil"
 )
 
 // TestSimpleLayerUpload covers the layer upload process, exercising common