Convert the remaining expect-based test scripts (phase1-6 runtime, usb,
wifi, bluetooth, dbus, greeter, live-iso, posix) to the stdlib python
harness, completing the migration started in 9ec00d4c81. Each script now
prefers booting the live ISO when present (falling back to harddrive.img
with snapshot=on), and retries up to 5 times when QEMU exits early or is
killed (rc 3 / 137) — the host-contention failure mode recorded in the
2026-07-20 runtime-proof status.
qemu-login-expect.py: treat an incomplete step sequence as a failure even
when a pass marker was seen partway through — partial sequences must not
count as a pass.
vasilito