* Move GetPsuInventory from Systems category to Chassis category
* Change get_psu_inventory to search through Chassis instead of Systems and PoweredBy for PowerSupplies
* Remove GetPsuInventory from Examples
* remove trailing whitespace
* Change boolean check from '!= None' to 'is not None'
* Don't include 'Absent' PSUs in get_psu_inventory()
* Add check to see if Power key is in Chassis before proceeding
* remove trailing whitespace
* Add continue step for when powersupply property is not found, and check if resulting entries is empty, returning message if nothing was found rather than an empty list