Healthcheck port is optional

As per commit 1d515dc6a4d6ac7d48c13ef6c2843f6dbd5bdd6a, but for the two
files introduced in e8e0eef9eea10ec53ba868c67e316220de9a877c.

Correct comment to state that the healthcheck port is optional as per:
https://github.com/alphagov/vcloud-edge_gateway/blob/e0c3685fc51b8b52de4871c7d314b86fe