labs: split get_base_disk_path
labs: split get_base_disk_path

Spin off get_base_disk_name from get_base_disk_path so we can get the
disk name without the directory.

Change-Id: Id813fd9bbf8a859b639f92a380c067dfc67a95c7

Nabs007/training-guides,openstack/training-guides,harrisonfeng/training-guides,harrisonfeng/training-guides,harrisonfeng/training-guides,openstack/training-guides,Nabs007/training-guides,Nabs007/training-guides