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[nova][ptg] pinned and unpinned CPUs in one instance


Agreements from the PTG:

How we will test it:
* do functional test with libvirt driver, like the pinned cpu tests we 
have today
* donyd's CI supports nested virt so we can do pinned cpu testing but 
not realtime. As this CI is still work in progress we should not block 
on this.
* coverage in a nice to 

Naming: use the 'shared' and 'dedicated' terminology

Support both the hw:pinvcpus=3 and the resources:PCPU=2 flavor extra 
specs syntaxtbut not in the same flavor. The resources:PCPU=2 syntax 
will have less expression power until nova models NUMA in placement. So 
nova will try to evenly distribute PCPUs between numa nodes. If it not 
possible we reject the request and ask the user to use the 
hw:pinvcpus=3 syntax.

Realtime mask is an exclusion mask, any vcpus not listed there has to 
be in the dedicated set of the instance.

TODOInvestigate whether we want to enable NUMA by default
* Pros: Simpler, everything is NUMA by default
* Cons: We'll either have to break/make configurablethe 1:1 guest:host 
NUMA mapping else we won't be able to boot e.g. a 40 core shared 
instance on a 40 core, 2 NUMA node host