WIP slapos.slap: Reorganise Hateaos code
Move Hateoas related code from core API to an separated file slapos.slap.hateoas which can be reusable. Move exceptions to slapos.slap.exceptions to be able to use on both files Move Hateoas code from https://lab.nexedi.com/nexedi/slapos.toolbox/blob/master/slapos/agent/tester.py into slapos core to make it reusable.