cpuid: Don't try to run the nokvm tests if host system is unknown

We don't know if disable_kvm=yes will really work, so don't try it if we
don't know the host system.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

qemu/tests/cfg/qemu_cpu.cfg

@@ -150,7 +150,7 @@
 
         #KNOWN BUG: RHEL-7.0 qemu-kvm doesn't show the -no-kvm option on -help,
         # so virt-test doesn't use the option and disable_kvm=yes doesn't work
-        no Host_RHEL.m7
+        no Host_RHEL.m7, qemu_flavor_unknown
 
     variants:
         - check_models: