Make Docker shut up

Makefile

@@ -35,7 +35,7 @@ $(image_tar): Dockerfile.test
 
 $(image_eif): $(image_tar)
 	@echo "Building $(image_eif)..."
-	@docker load -i $<
+	@docker load --quiet --input $<
 	@nitro-cli build-enclave \
 		--docker-uri $(image_tag) \
 		--output-file $(image_eif)