fix(xo-server/migration): don't loop if VM failed to migrate with CBT enabled

[fbeauchamp]

bug not reproduced on our lab apply the same patch as commit d2a897c3b88d478a04fef0fb75b809cacc80b97a

The disk attached to dom0 is a XAPI internal process, this commit ensure it is not taken into account when choosing a strategy to disable CBT

this commit also ensure the process is not stuck in infinite loop if the XAPI fail to disable CBT

Description

Short explanation of this PR (feel free to re-use commit message)

Checklist

• Commit
  • Title follows commit conventions
  • Reference the relevant issue (Fixes #007, See xoa-support#42, See https://...)
  • If bug fix, add Introduced by
• Changelog
  • If visible by XOA users, add changelog entry
  • Update "Packages to release" in CHANGELOG.unreleased.md
• PR
  • If UI changes, add screenshots
  • If not finished or not tested, open as Draft