If socket attribute is present we start VNC that listens only on that
unix socket. This makes the parser behave the same way as we actually
use the socket attribute.
Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
* Add a test for listen=XXX and <listen address=YYY/> collision error
* Add an explicit test for listen=XXX duplicated to <listen address=XXX/>
We implicitly test it elsewhere but I figure it's better to be explicit,
and this test case can be extended in the future for additional listen
back compat if/when we support <listen type='socket'/> syntax
