migrate-vm: strip CPU information from XML

[abizer]

when moving VMs from hypervisors with incompatible CPU types, we should strip the CPU type field from the KVM XML domain metadata so we can just start VMs easily without having to virsh edit <domname> to fix the CPU information.

[jvperrin]

+1 to this, could evenreplace it with the correct CPU type for the target hypervisor (for performance perhaps? Not sure how big the difference is there between generic and host CPUs)

[jvperrin]

Oh, also the title should be migrate-vm instead of makevm.