Move manifest package to schema1

As we begin our march towards multi-arch, we must prepare for the reality of
multiple manifest schemas. This is the beginning of a set of changes to
facilitate this. We are both moving this package into its target position where
it may live peacefully next to other manfiest versions.

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

notifications/http_test.go

@@ -10,7 +10,7 @@ import (
 	"strconv"
 	"testing"
 
-	"github.com/docker/distribution/manifest"
+	"github.com/docker/distribution/manifest/schema1"
 )
 
 // TestHTTPSink mocks out an http endpoint and notifies it under a couple of
@@ -75,12 +75,12 @@ func TestHTTPSink(t *testing.T) {
 		{
 			statusCode: http.StatusOK,
 			events: []Event{
-				createTestEvent("push", "library/test", manifest.ManifestMediaType)},
+				createTestEvent("push", "library/test", schema1.ManifestMediaType)},
 		},
 		{
 			statusCode: http.StatusOK,
 			events: []Event{
-				createTestEvent("push", "library/test", manifest.ManifestMediaType),
+				createTestEvent("push", "library/test", schema1.ManifestMediaType),
 				createTestEvent("push", "library/test", layerMediaType),
 				createTestEvent("push", "library/test", layerMediaType),
 			},