KVM host CPU model

[vholer]

Description
We gather KVM_MACHINES and KVM_CPU_MODELS to get supported (virtual) hardware specifications by the libvirt/QEMU. Regarding the KVM_CPU_MODELS, it's just a list of all available models, not the ones which can actually run on the machines.

It might be good to get also the actual hardware CPU model, which is closest to one of the available libvirt/QEMU CPU models:

virsh > capabilities
<capabilities>

  <host>
    <uuid>....</uuid>
    <cpu>
      <arch>x86_64</arch>
      <model>SandyBridge-IBRS</model>

the item is under CAPABILITIES/HOST/CPU/MODEL path.

Proposed parameter could be KVM_CPU_MODEL (without trailing s).

The extended machine models monitoring would look like:

KVM_MACHINES="pc-i440fx-rhel7.6.0 pc pc-i440fx-rhel7.0.0 ..."
KVM_CPU_MODELS="486 pentium pentium2 pentium3 pentiumpro coreduo ..."
KVM_CPU_MODEL="Skylake-Server-IBRS"

Use case
Better insight into what CPU model to choose (when not using the host passthrough).

Additional Context

Reference support ticket:
https://opennebula.zendesk.com/agent/tickets/11889

Progress Status

• Branch created
• Code committed to development branch
• Testing - QA
• Documentation
• Release notes - resolved issues, compatibility, known issues
• Code committed to upstream release/hotfix branches
• Documentation committed to upstream release/hotfix branches
  __

[al3xhh]

PRs to merge in master:

code: #3852
docs: OpenNebula/docs#806