Bug fix: servlet "bound_to" method called when HTTP service is ready

Avoids to consider the servlet accessible whereas the HTTP server is not yet listening
HTTP Service: Support for updated service properties

Improvement:
- When the path property of a servlet service is update, the servlet is
  re-registered with the new path

Bug fix:
- Servlet registration is effective only once the HTTP service is up & running
  => bound_to(...) is only called once the server is accessible
Removed the PYTHONPATH definition from the scripts

Calling python with the '-c' argument works better