qemu commit 13c6be96618c ("net: stream: add unix socket") introduces
support for native AF_UNIX support, finally making qrap useless.
We can't quite drop that yet until a qemu release includes it, and
then we'll need to wait a while for users to switch anyway, but at
least for tests, we can use that support.
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>