* Add GetManagerNicInventory command for Manager category, and tweak redfish_utils' get_nic_inventory to accommodate manager nic interfaces
* Remove get_manager_nic_inventory, since it is unnecessary while using get_manager in get_nic_inventory
* Rework get_nic_inventory() to take a resource_type as a string, which will be just the category parameter from redfish_facts, making it clearer
* remove extraneous blank line to conform with pep8
* Add GetManagerNicInventory example task to EXAMPLES docstring