Update "apology" page

[jmfee-usgs]

Our original intention for this page was to be shown when our servers were unreachable. However, it is shown when our servers send a 503 Service Unavailable HTTP status code.
https://github.com/usgs/earthquake-website/blob/master/src/htdocs/apology.html

This page should be updated to say something more accurate.

[lisa-usgs]

So will the message we put on this page be shown for all 500-series codes?

[jmfee-usgs]

Akamai shows this for 503 Service Unavailable responses, we can also configure it to be shown for other 5xx response codes.