testapp: return error on HW failure

in our CI setup for HW testing, we want QAT Engine to return an error code if the HW fails. Currently, we build a custom engine, with

```
--disable-qat_sw \
--with-qat_engine_id=qathwtest && \
```

There's an OpenSSL SW fallback controlled by `fallback_to_openssl = 1;` but toggling these to 0 still does not make QAT Engine/ testapp to return 1.

This issue is to get a build setup where HW failures can be reliably tested.