sanitytest: remove use of string.lower()
sanitytest: remove use of string.lower()

Call lower() directly on the string object instance, not
the class

Signed-off-by: Daniel P. Berrange <bb938cf255e055ff3507f2627d214e8e62118fcf@redhat.com>

libvirt/libvirt-python,libvirt/libvirt-python,libvirt/libvirt-python