Clarify interactive run-test completion messaging

[kergoth]

Summary

The container test runner's completion/status messaging is misleading in interactive single-distro sessions.

Problem

A command such as:

./script/test -r -i arch

can report Test completed for distro: arch even though the session was intentionally interactive rather than a straightforward non-interactive success/fail test run. That phrasing overstates what actually happened.

Goal

Adjust test/containers/run-test messaging so interactive modes describe the session accurately.

Done looks like

• Interactive shell or debug-oriented runs no longer emit a misleading generic success/completion message.
• The final status text distinguishes between:
  • non-interactive automated test completion
  • interactive shell/debug sessions
  • early-stop or partial-run modes
• The wording is clear for both single-distro and multi-distro runs.

Notes

This is a UX issue, but it matters because the current message can make a manual debugging session look like a completed automated validation.