[Tuner] Add tests to account for runtime failures

[kuhar]

The tuner invokes external tools like iree-compile and iree-benchmark-module. These may time out or fail. We should make sure that these failures are handled gracefully so that we don't lose tuning progress. By 'gracefully' I mean not aborting and, instead, either using some placeholder values or retrying a few times.

To accomplish this goal, we should have a robust test suite that checks for these failure modes.