Fix backend error when creating multiple templates

Backend fails when user tries to create multiple templetes using local
isos. The error occurs when Kimchi verifies if qemu has access to the
local iso. Kimchi creates a tmp VM for each iso, but, they have same
name and uuid, what causes the error.
This patch changes the uuid for each VM, fixing the problem.

Signed-off-by: Rodrigo Trujillo <rodrigo.trujillo@linux.vnet.ibm.com>