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>

vendor/github.com/opencontainers/runtime-spec/specs-go/state.go

@@ -0,0 +1,17 @@
+package specs
+
+// State holds information about the runtime state of the container.
+type State struct {
+	// Version is the version of the specification that is supported.
+	Version string `json:"ociVersion"`
+	// ID is the container ID
+	ID string `json:"id"`
+	// Status is the runtime state of the container.
+	Status string `json:"status"`
+	// Pid is the process ID for the container process.
+	Pid int `json:"pid"`
+	// BundlePath is the path to the container's bundle directory.
+	BundlePath string `json:"bundlePath"`
+	// Annotations are the annotations associated with the container.
+	Annotations map[string]string `json:"annotations,omitempty"`
+}