qemu-iotests: Use -nographic in 182

This avoids that random UI frontend error messages end up in the output.
In particular, we were seeing this line in CI error logs:

+Unable to init server: Could not connect: Connection refused
Signed-off-by: NKevin Wolf <kwolf@redhat.com>
Reviewed-by: NKashyap Chamarthy <kchamart@redhat.com>
Reviewed-by: NJeff Cody <jcody@redhat.com>

tests/qemu-iotests/182

@@ -62,7 +62,7 @@ _launch_qemu -drive file=$TEST_IMG,if=none,id=drive0,file.locking=on \
 
 echo
 echo "Starting a second QEMU using the same image should fail"
-echo 'quit' | $QEMU -monitor stdio \
+echo 'quit' | $QEMU -nographic -monitor stdio \
     -drive file=$TEST_IMG,if=none,id=drive0,file.locking=on \
     -device $virtioblk,drive=drive0 2>&1 | _filter_testdir 2>&1 |
     _filter_qemu |