bug(e2e): avoid rendering stale Kubernetes reports

[danehans]

User Story

As a contributor running Kubernetes E2E, I want reports to describe the current run so that I can trust the reported result.

Problem Statement

e2e/rust/e2e-kubernetes.sh renders results/e2e-kubernetes.html whenever the JUnit XML path exists, even when the current run skips Nextest and produces no JUnit output. A stale XML file can therefore be rendered as if it came from the current run. With a custom report name, the wrapper can also move stale default XML to the new report name.

Impact / Why This Matters

A stale report can misrepresent which tests ran and whether they passed. Contributors must manually compare timestamps or remove old artifacts before each run, which is easy to miss and undermines report reliability.

Acceptance Criteria

• Kubernetes E2E only moves or renders JUnit output produced by the current run.
• A conformance-only run does not create or rename XML/HTML reports from stale artifacts.
• Automated coverage exercises stale report files and a run that skips Nextest.

Reproduction Steps

1. Leave an existing results/e2e-kubernetes.xml from a previous Nextest run.
2. Run Kubernetes E2E with OPENSHELL_E2E_KUBERNETES_FEATURES="" so only CLI conformance runs.
3. Observe that the wrapper renders the old XML at the end of the new run.

Environment

• OpenShell: main at 0b351c4a9
• OS: macOS; the shell logic is platform-independent
• Runtime: Kubernetes E2E wrapper with Nextest disabled

[danehans]

/assign