check format / fix format: include ordering for unspecified directories

When adding an include from a directory not explicitly specified in our check_format scrips,
the automatic formatting fixing may produce output that gets flagged by the formatting check.
That's less then ideal. Ideally they would line up when there's no explicit ordering specified.

Context: https://github.com/envoyproxy/nighthawk/pull/493#pullrequestreview-476390192