If a binhost file sets a TTL header, honor it.

Reviewed-on: https://chromium-review.googlesource.com/225279
Reviewed-on: https://chromium-review.googlesource.com/225423
Tested-by: David James <davidjames@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Zac Medico <zmedico@gentoo.org>
Acked-by: Brian Dolbec <dolsen@gentoo.org>