Add some new variants/rules that will run some tests using
additional cpu_model_flags values. Especially:

 * CPU models that require "+apic" to be run on RHEL-6 hosts on Intel
   CPUs
 * CPU models that require "-abm,-sse4a" on Intel CPUs
 * CPU models that require using "-svm" because we don't enable nesting
   by default
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>