scripts/soak-test.sh claimed to isolate daemon coordination from
interactive sessions through a private CBM_CACHE_DIR, but only
CBM_RUNTIME_DIR moves the daemon rendezvous, so the soak shared the
operator's account daemon and asserted that its own shutdown stopped it.
Source scripts/test-runtime.sh for a harness-owned runtime and cache,
and let the helper stop the private daemon before the root is removed.
Add tests/test_soak_runtime_isolation_contract.sh, which fails before
this change, and wire it into scripts/test.sh.
Part of #1696.
Signed-off-by: Anton Standrik <astandrik@yandex-team.ru>
