Flush cache and wait more seconds before undocking drive bay
Check for firmware_node/status if bay is occupied

Dell Latitude BIOS/ACPI has bug which cause that docked attribute is always 0.
So check for firmware_node/status which is non zero when bay is occupied.
Note that on older kernels firmware_node/status is not available.
poweroff_drivebay(): show progress via "Powering off drive bay..." then "done."