Since this usb.py script is used to test
usb-storage device, rename it to usb_storage.py.
Also, as usb_storage.cfg is already consolidated
in usb.cfg, delete it.
Signed-off-by: NQingtang Zhou <qzhou@redhat.com>

A frequent request we've got from users is that the name
'kvm' makes assumptions that are not true for a lot of
the use cases of the test suite. Then let's rename
the subtest 'kvm' to 'qemu', making it more accurate.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>

Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>