tests: Teach qemuxml2argvtest about spapr-vio addresses

tests: Teach qemuxml2argvtest about spapr-vio addresses

We can't call qemuCapsExtractVersionInfo() from test code, because it
expects to be able to call the emulator, and for testing we have fake
emulators that can't be executed. For that reason qemuxml2argvtest.c
doesn't call qemuDomainAssignPCIAddresses(), instead it open codes its
own version.

That means we can't call qemuDomainAssignAddresses() from the test code,
instead we need to manually call qemuDomainAssignSpaprVioAddresses().

Also add logic to cope with qemuDomainAssignSpaprVioAddresses() failing,
so that we can write a test that checks for a known failure in there.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>