nVMX x86: "external-interrupt exiting" must be set if "virtual-interrupt delivery" is set

According to section "Checks on VMX Controls" in Intel SDM vol 3C,
the following check needs to be enforced on vmentry of L2 guests:

    If the "virtual-interrupt delivery" VM-execution control is 1, the
    "external-interrupt exiting" VM-execution control must be 1.

This unit-test validates the above vmentry check.

Signed-off-by: Krish Sadhukhan <krish.sadhukhan@oracle.com>
Reviewed-by: Karl Heubaum <karl.heubaum@oracle.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>