Comment 4 for bug 1899082

I traced this bug to hw/char/serial.c/serial_ioport_read

Bug disappears when I add qemu_log("serial_ioport_read %x %x\n", (int)addr, ret); into the end of this function.

I suppose that there is avocado (or socket) io synchronization problem, because running the same test without avocado works normally.