test: genericxml2xml: test graphics listen= compat
    
    * 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