Make CI script to verify that vendor is in sync

Signed-off-by: Odin Ugedal <odin@ugedal.com>

Makefile

@@ -1,7 +1,7 @@
 .PHONY: all shell dbuild man release \
 	    localtest localunittest localintegration \
 	    test unittest integration \
-	    cross localcross
+	    cross localcross vendor verify-dependencies
 
 CONTAINER_ENGINE := docker
 GO := go
@@ -112,13 +112,24 @@ clean:
 	rm -rf $(RELEASE_DIR)
 	rm -rf $(MAN_DIR)
 
-validate:
+validate: verify-dependencies
 	script/validate-gofmt
 	script/validate-c
 	$(GO) vet $(allpackages)
 
 ci: validate test release
 
+vendor:
+	export GO111MODULE=on \
+	$(GO) mod tidy && \
+	$(GO) mod vendor && \
+	$(GO) mod verify
+
+verify-dependencies: vendor
+	@test -z "$$(git status --porcelain -- go.mod go.sum vendor/)" \
+		|| (echo -e "git status:\n $$(git status -- go.mod go.sum vendor/)\nerror: vendor/, go.mod and/or go.sum not up to date. Run \"make vendor\" to update"; exit 1) \
+		&& echo "all vendor files are up to date."
+
 cross: runcimage
 	$(CONTAINER_ENGINE) run ${CONTAINER_ENGINE_RUN_FLAGS} -e BUILDTAGS="$(BUILDTAGS)" --rm -v $(CURDIR):/go/src/$(PROJECT) $(RUNC_IMAGE) make localcross