Adding config test before reload

ExecStartPre has nginx -t to test the Nginx config before starting
the service initially but ExecReload will just issue an Nginx reload
without testing the config first. If the config ends up being bad
this takes Nginx down. Perform a config test before reloading and if
that fails leave Nginx running on the previous config in RAM.

nginx/ng/files/nginx.service

@@ -7,6 +7,7 @@ Type=forking
 PIDFile=/run/nginx.pid
 ExecStartPre=/usr/sbin/nginx -t
 ExecStart=/usr/sbin/nginx
+ExecReload=/usr/sbin/nginx -t
 ExecReload=/usr/sbin/nginx -s reload
 ExecStop=/bin/kill -s QUIT $MAINPID
 Restart=on-failure