generatefeed: new helper script to easily create RSS2 Feeds from a bunch of well-formated JSON files

This first commit adds a script which generate a RSS feed from the statistics from rdiff-backup

It makes tests easiers and lighten the code in view.py

The code in the view is lighter, and the generic part could have been moved to utils

Doing so allows more grain control over the tests, as sup_process is just a
syntax sugar over RPC calls.

test / runner: new test for runSoftwareWithLock and runInstanceWithLock, which are both base functions of the webrunner

This also makes the function easier to test

  [agent] referer to an extra_requires which don't exist anymore

  Use json as configuration format
  Accept remote configuration file (url to a json)
  Introduce API to assert reponse codes and result for http and dns
  Add Unit tests.

Conflicts:
	setup.py

  This tool was originally released at http://git.erp5.org/gitweb/erp5.git/tree/HEAD:/erp5/util/webchecker?js=1 and modified by Romain Courteau later them.

  Now people can easily add tests

  slapos/builder was removed.