Don't call RetryFunction with nil.
Don't call RetryFunction with nil.

The bug was introduced by https://github.com/kubernetes/perf-tests/pull/467
These are two places I missed to update.

shyamjvs/perf-tests,sjug/perf-tests,sjug/perf-tests,shyamjvs/perf-tests,sjug/perf-tests,shyamjvs/perf-tests,kubernetes/perf-tests,kubernetes/perf-tests,shyamjvs/perf-tests,sjug/perf-tests,kubernetes/perf-tests,shyamjvs/perf-tests,sjug/perf-tests,kubernetes/perf-tests,kubernetes/perf-tests