--power_cycle_dut sometimes fails

[inductivekickback]

Sometimes the --power_cycle_dut operation fails to reset the DUT.

To reproduce:

• Select an example from the SDK that enters SYSTEM.OFF after some timeout (e.g. ble_app_uart)
• Program the example onto a DK (e.g. PCA10040) that has SB9 cut
• Attach the PPK to the DK and set the switches to use the DK's power supply
• Wait for the DUT to go into SYSTEM.OFF mode
• Perform an operation that includes --power_cycle_dut

[inductivekickback]

The same behavior happens when using the official nRF Connect GUI so this issue is probably a hardware problem.