x86: Add test for TPR threshold check on VM-entry

This test checks that a nested VM-entry fails if the "use TPR shadow"
VM-execution control is set, the "virtual-interrupt delivery"
VM-execution control is clear, and the TPR threshold is greater than
0xf.

Signed-off-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>