Use a null_resource to zip the lambda source

`files/rename_email_files_with_request_id.zip` is now created by a
`null_resource`. The resource is rebuilt when the source
(files/rename_email_files_with_request_id.py) is changed.

projects/email_alert_notifications/resources/email_alert_notifications.tf

@@ -41,13 +41,23 @@ resource "aws_iam_role_policy" "write_to_logs" {
   policy = "${file("templates/write_to_logs_policy.json")}"
 }
 
-resource "aws_lambda_function" "rename_email_files_with_request_id"{
-  filename = "rename_email_files_with_request_id.zip"
+resource "aws_lambda_function" "rename_email_files_with_request_id" {
+  depends_on = ["null_resource.build_rename_email_files_with_request_id"]
+  filename = "files/rename_email_files_with_request_id.zip"
   function_name = "rename_email_files_with_request_id"
   role = "${aws_iam_role.lambda_execute_and_write_to_email_alert_bucket.arn}"
   handler = "rename_email_files_with_request_id.lambda_handler"
   runtime = "python2.7"
-  source_code_hash = "${base64sha256(file("rename_email_files_with_request_id.zip"))}"
+  source_code_hash = "${base64sha256(file("files/rename_email_files_with_request_id.py"))}"
+}
+
+resource "null_resource" "build_rename_email_files_with_request_id" {
+  triggers {
+    source_code_hash = "${base64sha256(file("files/rename_email_files_with_request_id.py"))}"
+  }
+  provisioner "local-exec" {
+    command = "zip -j files/rename_email_files_with_request_id.zip files/rename_email_files_with_request_id.py"
+  }
 }