Fix for parallel port passthrough for QEMU

Fix for parallel port passthrough for QEMU

I came across a bug that the command line generated for passthrough
of the host parallel port /dev/parport0 by libvirt for QEMU is incorrect.

It currently produces:
-chardev tty,id=charparallel0,path=/dev/parport0
-device isa-parallel,chardev=charparallel0,id=parallel0

The first parameter is "tty". It sould be "parport".

If I launch qemu with -chardev parport,... it works as expected.

I have already filled a bug report (
https://bugzilla.redhat.com/show_bug.cgi?id=823879 ), the topic was
already on the list some months ago:

https://www.redhat.com/archives/libvirt-users/2011-September/msg00095.html

Signed-off-by: Eric Blake <eblake@redhat.com>