tests: Add virtio-9p qtest

Make it conditional to 9p availability.
Create a temporary directory to share.

Signed-off-by: Andreas Färber <afaerber@suse.de>
tests: Add pvpanic qtest

Signed-off-by: Andreas Färber <afaerber@suse.de>
qtest: Factor out qtest_qmp_receive()

Signed-off-by: Andreas Färber <afaerber@suse.de>
pvpanic-test: Assert pause event

Signed-off-by: Andreas Färber <afaerber@suse.de>
nvme: Permit zero-length block devices

It may not be sensible for normal use cases, but it allows to use
/dev/null in QTest.

Signed-off-by: Andreas Färber <afaerber@suse.de>
tests: Add nvme qtest

Signed-off-by: Andreas Färber <afaerber@suse.de>
tests: Add i82801b11 qtest

Signed-off-by: Andreas Färber <afaerber@suse.de>