use new iam variable in cloud function module

tests/modules/cloud_function/fixture/main.tf

@@ -0,0 +1,29 @@
+/**
+ * Copyright 2020 Google LLC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+module "test" {
+  source      = "../../../../modules/cloud-function"
+  project_id  = "my-project"
+  name        = "test"
+  bucket_name = var.bucket_name
+  bundle_config = {
+    source_dir  = "bundle"
+    output_path = "bundle.zip"
+  }
+  iam = {
+    "roles/cloudfunctions.invoker" = ["allUsers"]
+  }
+}