test fninit/fnstsw/fnstcw instructions emulation

Add test for fninit/fnstsw/fnstcw instructions emulation. This exact
code sequence is executed by Linux kernel during boot and sometimes gets
emulated by KVM.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>