VOL-1460 Updated core to use voltha-protos instead of local protos
Moved protos to python directory in order to maintain functionaly of containers built there.
Added capability to do local builds of protos
Added instructions on running dep ensure for getting protos.
Updated github.com/golang/protobuf version to v1.3.1

Change-Id: Ia6ef55f07f0d5dcb5b750d7c37b21b71db85bfc4
diff --git a/vendor/k8s.io/apimachinery/pkg/runtime/types.go b/vendor/k8s.io/apimachinery/pkg/runtime/types.go
index 1f7f662..eb284ea 100644
--- a/vendor/k8s.io/apimachinery/pkg/runtime/types.go
+++ b/vendor/k8s.io/apimachinery/pkg/runtime/types.go
@@ -43,6 +43,8 @@
 const (
 	ContentTypeJSON string = "application/json"
 	ContentTypeYAML string = "application/yaml"
+
+	ContentTypeProtobuf string = "application/vnd.kubernetes.protobuf"
 )
 
 // RawExtension is used to hold extensions in external versions.