Feature/kvm incremental backup

Blocker:

• capability to have SlapOS Master capable to directly deploy this branch on nodes to being able to test them gradually in real environments
• pick up qmpbackup >= 0.32 and adapt the system, as new important features came in
  • https://github.com/abbbi/qmpbackup/issues/17

Tasks:

• do tests like in theia, https://lab.nexedi.com/nexedi/slapos/-/merge_requests/1545#note_203808

Tools:

• qmpbackup

Research notes (to fill):

• install:
  • python3 -m venv qmpb
  • source qmpb/bin/activate
  • pip install https://github.com/abbbi/qmpbackup/releases/download/v0.29/qmpbackup-0.29.tar.gz
  • pip install qemu.qmp (this is a hack, maybe upstream 🐛 bugfix)
• backup
  • qmpbackup --socket ~/var/qmp_socket backup --compress --level auto --target ~/srv/qmpbackup/ --include virtio0
  • but:
    • qmpbackup --socket ~/var/qmp_socket backup --level auto --target ~/srv/qmpbackup-another/ --include virtio0
    • results with ERROR Bitmap exists, but target directory does not contain full backup.
    • so it is required to do qmpbackup --socket ~/var/qmp_socket backup --compress --level full --target ~/srv/qmpbackup-another/ --include virtio0, then with --level auto will work
      • maybe to report to upstream 🐛 with --force option or auto-full backup style, to backoff automatically to full mode if inc fails
• restore
  • restore=qmprestore-$(date '+%Y%m%d%H%M%S')
  • cp -a ~/srv/qmpbackup/ ~/srv/$restore
  • qmprebase rebase --dir ~/srv/$restore/virtio0
  • ls ~/srv/$restore/virtio0
    • will result with something like FULL-NNN-virtual.qcow2

Preparation:

• prove in the test that restoration with resiliency setup really works
  • will take-over work with slapproxy? --> yes it does

Implementation:

• use qmpbackup to do backups and support restoration on import restoration moment