qemu: Add a subtest nx.

Test whether nx(cpu) bit takes effect in guest.

Signed-off-by: Ken Cao <kcao@redhat.com>
Signed-off-by: Feng Yang <fyang@redhat.com>
KVM test: Rename the nx_exploit.py to nx.py
Signed-off-by: Jason Wang <jasowang@redhat.com>
Reviewed-by: Yolkfull Chow <yzhou@redhat.com>
qemu.tests.cfg: Add config file for nx.py script.

Signed-off-by: Feng Yang <fyang@redhat.com>
Signed-off-by: Cao, Chen <kcao@redhat.com>
KVM-TEST: use cfg to store the ", " on cpu flags
Signed-off-by: Xiaoqing Wei <xwei@redhat.com>