Edit Site not showing HTTPS form on Web cluster

Still doing internal testing on this as to whether more changes are necessary to get it working.

OK, yeah, there's more going on here.

web_cluster and web_pack do compensation for the ssl_enabled property, but nothing for https.

Additionally, something is going wrong with the server variables -- they are not being propogated properly on web clusters, so attempting to enable https on a site is causing it to attempt to call scripts in /.

Going to investigate more.

An alternative way to fix would be to teach web pack and web cluster about the https_enabled. Trying that in #2954727: web_pack and web_cluster https_enabled not propogated.

Coming back to this patch, since it looks like the logic has to go in hosting_https anyway.

Simplified patch by fixing hosting_https_get_servers() instead and checking whether the server is in the list instead of duplicating check code in multiple places.

For some reason, I have to enable certificate generation on the hostmaster for the actual certificate provisioning to work (even though the cluster that I'm actually running the test platform on does not include the hostmaster).

But other than that, deploying to clusters seems to operate OK.