BZ#251643: Allow to set the cpu pinning for creating domain with virt-manager.
As well as virt-install, I want to set the cpu pinning
at the time of creating domain with virt-manager.
And, because virtinst changeset 320 was committed,
I add the allocation setting of pCPU to virt-manager.
some notes are follows:
- This feature works with changeset of virtinst is 320 or later.
- The specification about the CPU pin parameter follows that of virt-install.
- This function can be used only for xen hypervisor.
- When 1 pCPU in xen hypervisor, this function is disabled.