The Unload a Device command provides a simple function to ensure a device is
unloaded. If the command completes successfully and unloads the device or the
device is not in a ready status (the status if already unloaded), the command
completes normally. Different completion message text describes the condition.
The command may be helpful when several save commands are used in a CL program
and it is not known what the device condition is at the end.