Function cleanup

test/integration/shared.js:119–123

(testErr)

function withCursor(cursor, body, done) {
  let clean = false;
  function cleanup(testErr) {
    if (clean) return;
    clean = true;
    return cursor.close(closeErr => done(testErr || closeErr));
  }
  try {
    body(cursor, cleanup);
  } catch (err) {