Nginx "limit_zone" directive no longer valid

[cconover]

Aegir's generated nginx.conf file uses the directive limit_zone, which was deprecated and removed from Nginx.

This is currently making Nginx not usable for Aegir-managed web servers because Nginx cannot start with the Aegir configuration.

[cconover]

Looking through the Aegir Nginx configuration template, I see that there is a consideration for this change. It does not seem as though $nginx_is_modern is getting set in my server environment. I will continue digging to determine whether this is just a problem with my cluster, or an actual bug.