integration: add upstream validator to OCI roundtrip tests

In order to make sure that we don't create invalid OCI images that are
consistently invalid, add additional checks to ensure that both of the
generated OCI images in the round-trip test are valid according to the
upstream validator.

This commit vendors the following packages (deep breath):
* oci/image-tools@7575a09363, which requires
* oci/image-spec@v1.0.0-rc4 [revendor, but is technically an update
  because I couldn't figure out what version was vendored last time]
* oci/runtime-spec@v1.0.0-rc4
* xeipuuv/gojsonschema@6b67b3fab7
* xeipuuv/gojsonreference@e02fc20de9
* xeipuuv/gojsonpointer@e0fe6f6830
* camlistore/go4@7ce08ca145

Signed-off-by: Aleksa Sarai <asarai@suse.de>

integration/copy_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"fmt"
 	"io/ioutil"
+	"log"
 	"net/http"
 	"net/http/httptest"
 	"os"
@@ -13,6 +14,7 @@ import (
 	"github.com/containers/image/manifest"
 	"github.com/go-check/check"
 	"github.com/opencontainers/go-digest"
+	"github.com/opencontainers/image-tools/image"
 )
 
 func init() {
@@ -216,7 +218,14 @@ func (s *CopySuite) TestCopyOCIRoundTrip(c *check.C) {
 	out := combinedOutputOfCommand(c, "diff", "-urN", oci1+"/blobs", oci2+"/blobs")
 	c.Assert(out, check.Equals, "")
 
+	// For some silly reason we pass a logger to the OCI library here...
+	logger := log.New(os.Stderr, "", 0)
+
 	// TODO: Verify using the upstream OCI image validator.
+	err = image.ValidateLayout(oci1, nil, logger)
+	c.Assert(err, check.IsNil)
+	err = image.ValidateLayout(oci2, nil, logger)
+	c.Assert(err, check.IsNil)
 
 	// Now verify that everything is identical. Currently this is true, but
 	// because we recompute the manifests on-the-fly this doesn't necessarily