* Use an IP address for Google instance metadata

Makes Spilo start even if external DNS queries from
within the container are not working.

Do not continue with the startup when /etc/service is missing.

Per https://github.com/zalando/spilo/issues/511



* Follow Python guidelines on on-line comments
Co-authored-by: Alexander Kukushkin <cyberdemn@gmail.com>

* Extra space to the shell comment for readability
Co-authored-by: Alexander Kukushkin <cyberdemn@gmail.com>