svm: Verify the effect of V_INTR_MASKING on INTR interrupts

The test confirms the influence of the V_INTR_MASKING bit
on RFLAGS.IF. The expectation is while running a guest
with V_INTR_MASKING cleared to zero:

- EFLAGS.IF controls both virtual and physical interrupts.

While running a guest with V_INTR_MASKING set to 1:

- The host EFLAGS.IF at the time of the VMRUN is saved and
  controls physical interrupts while the guest is running.

- The guest value of EFLAGS.IF controls virtual interrupts only.

As discussed previously, this patch also modifies the vmrun
loop ( test_run ) to allow running with HIF=0

Signed-off-by: Cathy Avery <cavery@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>