Use system.getHostname() everywhere
Replace os.environ['HTTP_HOST'] with system.getHostname(), as a
result we do not crash when 'HTTP_HOST' is unset now.
# Directions for web crawlers.
# See http://www.robotstxt.org/wc/norobots.html.
User-agent: HTTrack
User-agent: puf
User-agent: MSIECrawler
User-agent: Nutch
Disallow: /