Add qtest for vhost-user

Add qtest for vhost-user

This test creates a 'server' chardev to listen for vhost-user messages.
Once VHOST_USER_SET_MEM_TABLE is received it mmaps each received region,
and read 1k bytes from it. The read data is compared to data from readl.

The test requires hugetlbfs to be already mounted and writable. The mount
point defaults to '/hugetlbfs' and can be specified via the environment
variable QTEST_HUGETLBFS_PATH.

The rom pc-bios/pxe-virtio.rom is used to instantiate a virtio pcicontroller.

Signed-off-by: Antonios Motakis <a.motakis@virtualopensystems.com>
Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
MST: fix up coding style
MST: disable vhost test temporarily

This test needs a bit more work: issues have been
found on legacy systems, disable it for now to
avoid false positives for people.
Will re-enable after issues are addressed.

Reported-by: Igor Mammedov <imammedo@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>