qemu.tests.cfg: Update iommu value in sr_iov.cfg

Cause Property 'pci-assign.iommu' doesn't take value '0'.

Signed-off-by: Shuping Cui <scui@redhat.com>
qemu.tests: Small bug fix for sr_iov_hotplug_negative

pci_addr option already used by usb controller,
so change name to pci_invaild_addr.

Signed-off-by: Shuping Cui <scui@redhat.com>