Fix srcache fetch status in logs

[dhsathiya]

Replace: upstream_cache_status with srcache_fetch_status

 log_format rt_cache '$remote_addr $upstream_response_time $srcache_fetch_status [$time_local] '
 '$http_host "$request" $status $body_bytes_sent '
 '"$http_referer" "$http_user_agent"'
 ' $request_time' ;

Check upstream_response_time as well.

[mrrobot47]

$upstream_response_time will only come when cache is not hit, hence makes the log look a little non-uniform. So moving it to the end near $request_time.