Add new <devnode> top-level <device> element, that list the associated
/dev files. Distinguish the main /dev name from symlinks with a 'type'
attribute of value 'dev' or 'symlink'.

Update a test to check XML schema, and actually add it to the test list
since it was missing.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>