test(vmop): add e2e tests for VMOP superseding

[danilrwx]

Description

Adds e2e coverage for the Superseded VMOP phase introduced in #2492.

Two deterministic scenarios verify that a non-terminal VMOP transitions to the
Superseded phase (with condition Completed, reason Superseded) when a newer
conflicting VMOP arrives for the same VM:

• Start superseded by Stop — the VM is pinned to a non-existent node, so its
  launcher pod stays Unschedulable and the Start VMOP never leaves InProgress.
• Migrate superseded by Stop — the migration target is pinned to a non-existent
  node, so the target pod stays Unschedulable and the Migrate VMOP stays in
  Scheduling/InProgress.

Both tests run under Label(precheck.NoPrecheck).

Why do we need it, and what problem does it solve?

The Superseded phase (#2492) shipped without e2e coverage. The hard part of
testing superseding is timing: the operation being superseded must still be
non-terminal when the superseding VMOP arrives. A fast workload (e.g. an Alpine
VM that migrates in seconds) makes such a test inherently racy.

Pinning the workload to a non-existent node removes the race entirely: the
launcher / migration target pod is permanently Unschedulable, so the
superseded operation stays in a non-terminal phase for as long as needed,
without sleeps or stress generators.

What is the expected result?

cd test/e2e && FOCUS=VirtualMachineSupersede task run

Both specs pass:

Ran 2 of 105 Specs
SUCCESS! -- 2 Passed | 0 Failed

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: test
type: chore
summary: Add e2e tests for VMOP superseding.
impact_level: low