For backward compatibility we used to add the tty path as
a tty attribute on console of type pty, duplicating the value
now found in source/@path, but the Relax-NG grammar wasn't
extended for this
<console type='pty' tty='/dev/pts/8'>
<source path='/dev/pts/8'/>
<target port='0'/>
</console>
* docs/schemas/domain.rng: allow an optional tty attribute
containing a devicePath