virDomainDefParseXML: Check for malicious cpu ids in <numa/>

virDomainDefParseXML: Check for malicious cpu ids in <numa/>

https://bugzilla.redhat.com/show_bug.cgi?id=1176020

Some users think this is a good idea:

      <vcpu placement='static'>4</vcpu>
      <cpu mode='host-model'>
        <model fallback='allow'/>
        <numa>
          <cell id='0' cpus='0-1' memory='1048576' unit='KiB'/>
          <cell id='1' cpus='9-10' memory='2097152' unit='KiB'/>
        </numa>
      </cpu>

It's not. Lets therefore introduce a check and discourage them in
doing so.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>