Resistance to hazardous slave parameters
As caddy-frontend SR is used in context where one master servers many slaves, over which the master owner does not have proper control, the SR needs to be resistent to slave parameters being hazardeous. In other software releases it is ok for buildout to fail or for the whole/part of the system to be disfunctional in case of wrong parameters, as requester will be in charge of fixing it. Here it is not the case.
This work consist of reviewing and checking all possibly dangerous slave parameters, which result in malfunction of the whole partition (master or slave) and introduces protection for each case.
Test results: PASS
Depends on: https://lab.nexedi.com/nexedi/slapos/merge_requests/398 MERGED