tests: turn skipLegacyCPUs into a flag
tests: turn skipLegacyCPUs into a flag

Make it obvious when it is used intentionally and error
out when used in combination with real capabilities.

Signed-off-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

fabianfreyer/libvirt,jfehlig/libvirt,nertpinx/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,olafhering/libvirt,zippy2/libvirt,eskultety/libvirt,jardasgit/libvirt,zippy2/libvirt,andreabolognani/libvirt,jardasgit/libvirt,zippy2/libvirt,crobinso/libvirt,eskultety/libvirt,fabianfreyer/libvirt,libvirt/libvirt,nertpinx/libvirt,nertpinx/libvirt,eskultety/libvirt,fabianfreyer/libvirt,eskultety/libvirt,crobinso/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,libvirt/libvirt,jardasgit/libvirt,nertpinx/libvirt,olafhering/libvirt,zippy2/libvirt,jardasgit/libvirt,crobinso/libvirt,libvirt/libvirt,jfehlig/libvirt,olafhering/libvirt,andreabolognani/libvirt,eskultety/libvirt,jfehlig/libvirt,crobinso/libvirt,jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,nertpinx/libvirt,jardasgit/libvirt