Use yaml config for various fpm settings.

  - Use instance config for `default_timeout` instead of global `init_config`
  - Migrate the following values into fpm status:
    - `fpm_status_uri`: which http endpoint to hit
    - `fpm_request_method`: which http request method to use
    - `fpm_hostname`: which fpm hostname to use
    - `fpm_port`: which fpm port ot hit