This make usage of the relationfield nicer.

See merge request nexedi/slapos.core!596

See merge request nexedi/slapos.core!595

When an user belonged to a group before running slapformat, the user was previously
removed from that group. This commit avoids it by simply appending SlapOS
additional groups.

  This API will be refactored on the new API

See merge request !591

   In the case of checkNotCycle, the re-recheck would always fail on a disconnected tree first, so it is mandatory patch the checkConnected (to skip) during the tests.

See merge request nexedi/slapos.core!579

- change url parameters for dispatch link
- use monitoring app landing url
- add url-user-pass parameters to monitor url

See merge request nexedi/slapos.core!592

See merge request nexedi/slapos.core!590

See merge request nexedi/slapos.core!589

have them deleted afterwards.

e2e.py, used for slapos/software/end-to-end-testing, can be given to a
testnode to run end-to-end-tests by requesting real instances.

See merge request nexedi/slapos.core!588

  It seems to define multiple entries leads to multiple attempts to install the all bt5s.

See merge request nexedi/slapos.core!586

  Otherwise printout may fail to print.

   This allow the sites to work w/o payzen or wechat preconfigured.

   Return None rather them raise, to allow the site to show an alternative page or inform that payments are disabled.