To sync with virDomainControllerModelUSB, we add two models
in qemuControllerModelUSB 'qusb1' and 'qusb2', but those
models are not supported in qemu driver. So add check in
device post parse to report errors if 'qusb1' and 'qusb2'
are specified.
Signed-off-by: NChunyan Liu <cyliu@suse.com>