Current PCI addresses are allocated at time of VM startup.
To make them truely persistent, it is neccessary to do this
at time of virDomainDefine/virDomainCreate. The code in
qemuStartVMDaemon still remains in order to cope with upgrades
from older libvirt releases
* src/qemu/qemu_driver.c: Rename existing qemuAssignPCIAddresses
to qemuDetectPCIAddresses. Add new qemuAssignPCIAddresses which
does auto-allocation upfront. Call qemuAssignPCIAddresses from
qemuDomainDefine and qemuDomainCreate to assign PCI addresses that
can then be persisted. Don't clear PCI addresses at shutdown if
they are intended to be persistent