KVM: selftests: x86: clarify what is reported on KVM_GET_MSRS failure

When KVM_GET_MSRS fail the report looks like

==== Test Assertion Failure ====
  lib/x86_64/processor.c:1089: r == nmsrs
  pid=28775 tid=28775 - Argument list too long
     1	0x000000000040a55f: vcpu_save_state at processor.c:1088 (discriminator 3)
     2	0x00000000004010e3: main at state_test.c:171 (discriminator 4)
     3	0x00007fb8e69223d4: ?? ??:0
     4	0x0000000000401287: _start at ??:?
  Unexpected result from KVM_GET_MSRS, r: 36 (failed at 194)

and it's not obvious that '194' here is the failed MSR index and that
it's printed in hex. Change that.
Suggested-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

tools/testing/selftests/kvm/lib/x86_64/processor.c

@@ -1085,7 +1085,7 @@ struct kvm_x86_state *vcpu_save_state(struct kvm_vm *vm, uint32_t vcpuid)
 	for (i = 0; i < nmsrs; i++)
 		state->msrs.entries[i].index = list->indices[i];
 	r = ioctl(vcpu->fd, KVM_GET_MSRS, &state->msrs);
-        TEST_ASSERT(r == nmsrs, "Unexpected result from KVM_GET_MSRS, r: %i (failed at %x)",
+        TEST_ASSERT(r == nmsrs, "Unexpected result from KVM_GET_MSRS, r: %i (failed MSR was 0x%x)",
                 r, r == nmsrs ? -1 : list->indices[r]);
 
 	r = ioctl(vcpu->fd, KVM_GET_DEBUGREGS, &state->debugregs);