Issue: Nova doesn't appear to handle the 'policy' specified for CPU features by libvirt, resulting in hypervisors indicating they require more features than they actually do when requesting a live migration.

$ virsh capabilities > temp
$ virsh cpu-baseline temp
<cpu mode='custom' match='exact'>
  <model fallback='allow'>Cascadelake-Server</model>
  <vendor>Intel</vendor>
  <feature policy='require' name='ds'/>
  <feature policy='require' name='acpi'/>
  <feature policy='require' name='ss'/>
  <feature policy='require' name='ht'/>
  <feature policy='require' name='tm'/>
  <feature policy='require' name='pbe'/>
  <feature policy='require' name='dtes64'/>
  <feature policy='require' name='monitor'/>
  <feature policy='require' name='ds_cpl'/>
  <feature policy='require' name='vmx'/>
  <feature policy='require' name='smx'/>
  <feature policy='require' name='est'/>
  <feature policy='require' name='tm2'/>
  <feature policy='require' name='xtpr'/>
  <feature policy='require' name='pdcm'/>
  <feature policy='require' name='dca'/>
  <feature policy='require' name='tsc_adjust'/>
  <feature policy='require' name='intel-pt'/>
  <feature policy='require' name='pku'/>
  <feature policy='require' name='md-clear'/>
  <feature policy='require' name='stibp'/>
  <feature policy='require' name='arch-capabilities'/>
  <feature policy='require' name='xsaves'/>
  <feature policy='require' name='invtsc'/>
  <feature policy='require' name='rdctl-no'/>
  <feature policy='require' name='ibrs-all'/>
  <feature policy='require' name='skip-l1dfl-vmentry'/>
  <feature policy='require' name='mds-no'/>
  <feature policy='require' name='tsx-ctrl'/>
  <feature policy='disable' name='hle'/>
  <feature policy='disable' name='rtm'/>
</cpu>


## CPU section from 'virsh capabilities'

    <cpu>
      <arch>x86_64</arch>
      <model>Cascadelake-Server-noTSX</model>
      <vendor>Intel</vendor>
      <microcode version='83886124'/>
      <counter name='tsc' frequency='2499999000' scaling='no'/>
      <topology sockets='1' cores='20' threads='2'/>
      <feature name='ds'/>
      <feature name='acpi'/>
      <feature name='ss'/>
      <feature name='ht'/>
      <feature name='tm'/>
      <feature name='pbe'/>
      <feature name='dtes64'/>
      <feature name='monitor'/>
      <feature name='ds_cpl'/>
      <feature name='vmx'/>
      <feature name='smx'/>
      <feature name='est'/>
      <feature name='tm2'/>
      <feature name='xtpr'/>
      <feature name='pdcm'/>
      <feature name='dca'/>
      <feature name='osxsave'/>
      <feature name='tsc_adjust'/>
      <feature name='cmt'/>
      <feature name='intel-pt'/>
      <feature name='pku'/>
      <feature name='ospke'/>
      <feature name='md-clear'/>
      <feature name='stibp'/>
      <feature name='arch-capabilities'/>
      <feature name='xsaves'/>
      <feature name='mbm_total'/>
      <feature name='mbm_local'/>
      <feature name='invtsc'/>
      <feature name='rdctl-no'/>
      <feature name='ibrs-all'/>
      <feature name='skip-l1dfl-vmentry'/>
      <feature name='mds-no'/>
      <feature name='tsx-ctrl'/>
      <pages unit='KiB' size='4'/>
      <pages unit='KiB' size='2048'/>
      <pages unit='KiB' size='1048576'/>
    </cpu>




## Resulting CPU Info Stored In Galera

{"arch": "x86_64", "model": "Cascadelake-Server-noTSX", "vendor": "Intel", "topology": {"cells": 1, "sockets": 1, "cores": 20, "threads": 2}, "features": ["sep", "rdtscp", "clflush", "mtrr", "avx512cd", "tsc", "pat", "tsc_adjust", "xsave", "clflushopt", "movbe", "pcid", "mpx", "3dnowprefetch", "pdcm", "ht", "skip-l1dfl-vmentry", "cmov", "fsgsbase", "avx2", "fma", "x2apic", "hle", "sse2", "ss", "est", "md-clear", "msr", "syscall", "xtpr", "lm", "popcnt", "acpi", "aes", "ibrs-all", "mca", "clwb", "xsaves", "arch-capabilities", "pclmuldq", "nx", "pni", "invpcid", "pge", "pse", "apic", "pbe", "smap", "bmi1", "sse4.2", "stibp", "dca", "monitor", "abm", "avx512f", "cx8", "fxsr", "erms", "lahf_lm", "pku", "sse", "rtm", "pse36", "vme", "avx512vnni", "pdpe1gb", "smx", "adx", "cx16", "rdrand", "smep", "mce", "f16c", "rdseed", "avx512vl", "mds-no", "rdctl-no", "xgetbv1", "tsx-ctrl", "avx", "avx512bw", "pae", "ds", "tm", "vmx", "sse4.1", "invtsc", "xsavec", "intel-pt", "tsc-deadline", "avx512dq", "de", "bmi2", "dtes64", "arat", "fpu", "xsaveopt", "mmx", "ssse3", "tm2", "spec-ctrl", "ssbd", "ds_cpl"]}


## Related Nova code

https://github.com/openstack/nova/blob/655cd30c9fd1753323f725f45581a56f1d17c075/nova/virt/libvirt/config.py#L670