Find the `expected` line within `times` trials.

        Args:
            expected    str: the expected string
            times       int: number of trials

def _expect(self, expected, times=50):
        """Find the `expected` line within `times` trials.

        Args:
            expected    str: the expected string
            times       int: number of trials
        """
        logger.debug('[%s] Expecting [%s]', self.port, expected)
        retry_times = 10
        while times:
            if not retry_times:
                break

            line = self._readline()

            if line == expected:
                return

            if not line:
                retry_times -= 1
                time.sleep(0.1)

            times -= 1

        raise Exception('failed to find expected string[%s]' % expected)