verx: report error if console is not supported

$ verx console test --uri=test:///default --transport=tls --host=iopl
{error,[3,0,
        <<"this function is not supported by the connection driver: virDomainOpenConsole">>,
        2,void,
        <<"this function is not supported by the connection driver: %s">>,
        <<"virDomainOpenConsole">>,void,-1,-1,void]}