Rename the exist config attribute: [libvirt]/cpu_model to
[libvirt]/cpu_models, which is an orderded list of CPU models the host
supports. The value in the list can be made case-insensitive.
Change logic of method: '_get_guest_cpu_model_config', if cpu_mode is
custom and cpu_models set. It will parse the required traits
associated with the CPU flags from flavor extra_specs and select the
most appropriate CPU model.
Add new method 'get_cpu_model_names' to host.py. It will return a list
of the cpu models that the CPU arch can support.
Update the docs of hypervisor-kvm.
Change-Id: I06e1f7429c056c4ce8506b10359762e457dbb2a0
Implements: blueprint cpu-model-selection
f80e5f989d