Change proxy_cache options depending on status code received

[Serban Teodorescu]

I should also add that currently this works really well for every distinct $request_url by:


location / {
	…
	error_page 500 502 503 504 /maintenance.html;
	…
	proxy_cache_valid 500 502 503 504 3m;
}

location = /maintenance.html {
	root /etc/nginx/static;
}