Live migration with Train-style cpu_shared_set not updating CPU pinning

In pre-Train times, when live migrating an instance without a CPU policy (and therefore without a NUMA topology) to a dest with a vcpu_pin_set, or to a dest with a vcpu_pin_set different from the source, the instance's CPU pinning information was not updated.

Now that CPU resources are a thing, and we use cpu_dedicated_set and cpu_shared_set (the version with the new meaning, not the old cpu_shared_set), this is still a problem. IOW, live migrating a VM with no CPU policy and no NUMA topology from cpu_shared_set=0,1 to cpu_shared_set=2,3 will leave it pinned to CPUs 0,1.