Allow to Add CPU or RAM in hotplug mode, without need of restart qemu process

/reviewed-on nexedi/slapos!175

/reviewed-on nexedi/slapos!172

Check that backup kvm disk is not corrupted

In order to work in deep directory structures it is required to have
kvm-controller script wrapped to avoid shabang limit.

  Make the integration with erp5testnode separeted from original SR.
  Optimise KVM resilient tests by downloading the test image on the software release site,
  without change the original SR. (This will sabe internet and speed up result).

  The image still way too big but it is better the whole image

  This is just cosmetics.

  This fixes bugs on the order of parts and duplicated sections introduced on:
    8d28b7e0
    d3df3b6e

Otherwise, performances get awful on HDD, and not far better on SSD.

Revert "resilient: new paramater to define the time to sleep before running the backup in the cron job."

This reverts commit 30d1a937.

Default is a random value between 0 and 6 hours. KVM and Slaprunner test instances set it at 0.