Add make target to generate CRI files

The cri make target generates the api.pb.go files by first fetching the
latest proto files from upstream and uses protoc to generate them.

Makefile

@@ -1,4 +1,4 @@
-.PHONY: all deps static clean realclean client-lint client-test client-sync backend frontend shell lint ui-upload
+.PHONY: all cri deps static clean realclean client-lint client-test client-sync backend frontend shell lint ui-upload
 
 # If you can use Docker without being root, you can `make SUDO= <target>`
 SUDO=$(shell docker info >/dev/null 2>&1 || echo "sudo -E")
@@ -45,6 +45,16 @@ IMAGE_TAG=$(shell ./tools/image-tag)
 
 all: $(SCOPE_EXPORT)
 
+update-cri:
+	curl https://raw.githubusercontent.com/kubernetes/kubernetes/master/pkg/kubelet/apis/cri/runtime/v1alpha2/api.proto > cri/runtime/api.proto
+
+protoc-gen-gofast:
+	@go get -u -v github.com/gogo/protobuf/protoc-gen-gofast
+
+# Use cri target to download latest cri proto files and regenerate CRI runtime files. 
+cri: update-cri protoc-gen-gofast
+	@cd $(GOPATH)/src;protoc --proto_path=$(GOPATH)/src --gofast_out=plugins=grpc:. github.com/weaveworks/scope/cri/runtime/api.proto
+
 docker/weave:
 	curl -L https://github.com/weaveworks/weave/releases/download/v$(WEAVENET_VERSION)/weave -o docker/weave
 	chmod u+x docker/weave