Switch to certificate in Docker file itself

* Don't ssh and run a local server as a separate ssh connexion anymore. This
  was risky and racy. Now, the local server is started on container startup,
  only if there is a hostname defined for it. Match with the correspondant
  certificate.
* Add to Dockerfile the certificate file and generate the client list so that
  udtc, as a client, can fetch the android files.
* Run in async mode (background) some command in udtc directory helper. This is
  used for this local server
Various cleanups and pep8 fixes