Move HTTPS configuration out of default Nginx template

I noticed that some HTTPS settings are set server-wide in the global Nginx template, which seems strange because HTTPS may not be enabled. Wouldn't it be better to move this to HTTPS-enabled vhosts? It could be that there was a good reason things were set up like this, but I'm sure what it would be.

If we don't have a good reason for it, let's move it out of Provision, and into Aegir HTTPS.

It we still need to support hosting_ssl, we can move it there too, but it's deprecated so I'd rather we didn't put our efforts there. (Nobody's been doing any work on it.) See #2751801: Deprecate SSL in core (to be re-integrated later) for that status of that.

From http/Provision/Config/Nginx/server.tpl.php:

 ## SSL performance
  ssl_session_cache   shared:SSL:10m;

<?php if ($satellite_mode == 'boa'): ?>
 ## SSL protocols, ciphers and settings
  ssl_protocols TLSv1.1 TLSv1.2;
  ssl_ciphers ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-DSS-AES128-GCM-SHA256:kEDH+AESGCM:ECDHE-RSA-AES128-SHA256:ECDHE-ECDSA-AES128-SHA256:ECDHE-RSA-AES128-SHA:ECDHE-ECDSA-AES128-SHA:ECDHE-RSA-AES256-SHA384:ECDHE-ECDSA-AES256-SHA384:ECDHE-RSA-AES256-SHA:ECDHE-ECDSA-AES256-SHA:DHE-RSA-AES128-SHA256:DHE-RSA-AES128-SHA:DHE-DSS-AES128-SHA256:DHE-RSA-AES256-SHA256:DHE-DSS-AES256-SHA:DHE-RSA-AES256-SHA:AES128-GCM-SHA256:AES256-GCM-SHA384:AES128-SHA256:AES256-SHA256:AES128-SHA:AES256-SHA:AES:CAMELLIA:DES-CBC3-SHA:!aNULL:!eNULL:!EXPORT:!DES:!RC4:!MD5:!PSK:!aECDH:!EDH-DSS-DES-CBC3-SHA:!EDH-RSA-DES-CBC3-SHA:!KRB5-DES-CBC3-SHA;
  ssl_prefer_server_ciphers  on;