update stalled-mysql tests to match new behavior

All wsapi operations now require the database (to update+check the
superSessionToken), so some tests that previously expected operations to
succeed without a database now expect them to fail (generally 503).

wsapi_client.js was changed to pass HTTP errors during
/wsapi/session_context back to the caller, so their response code can be
checked, rather than throwing an error (and preventing any other
assertions from being made).