CA-35407: Improve error message on VM.revert failure.
CA-35407: Improve error message on VM.revert failure.

On VM.revert, when the snapshot chain is too long to clone the snapshoted disks what we are reverting to, then propagate the SM backend error back to the user.

Signed-off-by: Thomas Gazagnaire <d17b540e4bd20a6d2c62b93674760725b3f75517@citrix.com>

koushikcgit/xcp-rrdd,koushikcgit/xcp-networkd,koushikcgit/xcp-networkd,djs55/xcp-rrdd,djs55/squeezed,sharady/xcp-networkd,robhoes/squeezed,johnelse/xcp-rrdd,simonjbeaumont/xcp-rrdd,koushikcgit/xcp-rrdd,koushikcgit/xcp-rrdd,simonjbeaumont/xcp-rrdd,sharady/xcp-networkd,djs55/xcp-rrdd,djs55/xcp-networkd,djs55/xcp-networkd,johnelse/xcp-rrdd