update cpu pinning configs for Train

[Edward Hope-Morley]

Since around the Queens timeframe Openstack supports moving Qemu emulator threads to a pool of non-pinned cores in nova-compute. This is particularly important when pinning vcpus using isolcpus so we should allow the charm to be able to configure it.

The way that pinning is configured in general has changed radically as of the Train release so in order to implement this change will require migrating the existing configs to Train first [1].

Note that one of the motivations for the changes introduced in Train was to make pinned cores and their associations trackable in Placement and as such there is a new way to configure flavors to leverage pinning that should be observed for Train+ deployments once this lands.

[1] https://specs.openstack.org/openstack/nova-specs/specs/train/approved/cpu-resources.html

[Edward Hope-Morley (hopem)]

Turns out this has already been implemented in the charm but i missed it because there was no LP bug associated with the change - https://github.com/openstack/charm-nova-compute/commit/7874696473b1332ab2875e801c42f35ac7d1868a. Its also released as part of the 20.02 release.