In platform_ServoPowerStateController, the test for
"start in recovery mode, then turn off" includes an
unnecessary and unexplained call to sleep:
        logging.info('Power DUT off in recovery mode without booting.')
        self.host.servo.switch_usbkey('off')
        self.controller.power_on(self.controller.REC_ON)
        time.sleep(10)
        self.controller.power_off()
        self.assert_dut_off('power_state:off failed at recovery screen ')

The call was allowing some Braswell-based boards to pass when
they really shouldn't have, at least occasionally.

There's no reason for the sleep() call; 'power_state:rec power_state:off'
is expected to work without requiring an intermediate delay.

Additionally, the test lines above are only run in the case where
a USB stick is present, but that test case can reasonably run when
the stick is absent.

The code should be updated to move the code to the "test_with_usb_unplugged()"
section of the code, and should test these two assertions:
  * power_state:rec followed by power_state:off without a delay leaves the
    DUT off.
  * After power_state:rec the DUT stays offline for the test's standard
    interval (30 seconds), and the DUT stays off after applying
    power_state:off.