Unify nginx configuration

This creates a simple base configuration skeleton, that other configuration can be easily loaded into.

ansible/roles/dokku/files/nginx.conf

@@ -1,29 +1,12 @@
-worker_processes  auto;
+ # Block requests which don't have an explicit handler
+server {
+    listen 80 default_server;
+    listen [::]:80 default_server;
 
-events {
-    worker_connections  1024;
+    server_name _;
+    access_log off;
+    return 418;
 }
 
-http {
-    include       /etc/nginx/mime.types;
-    default_type  application/octet-stream;
-
-    sendfile        on;
-
-    keepalive_timeout  65;
-
-    gzip  on;
-
-    # Block requests which don't have an explicit handler
-    server {
-        listen 80 default_server;
-        listen [::]:80 default_server;
-
-        server_name _;
-        access_log off;
-        return 418;
-    }
-
-    # Load configuration files for the default server block.
-    include /etc/nginx/conf.d/*.conf;
-}
+# Load configuration files for the default server block (this directory is used by dokku).
+include /etc/nginx/conf.d/*.conf;