[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.

It's not needed anymore to create a user at first launch of webrunner. Credential can be created from slapos recipe directly.
Webrunner can also clone default repository at first launch.

/reviewed-on nexedi/slapos.toolbox!7

  Also don't interrupt of parse command output fails

the process if older than dependency set.