emulator: test long-mode lidt/lgdt

A bug in kvm caused it to fail on long-mode lidt/lgdt.  This patch tests for
the failure.

However, kvm doesn't allow lidt/lgdt from mmio, so the test is disabled.

Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>