Investigate upgrade E2E test flaking

e.g. [[1]](https://app.wercker.com/Oracle/mysql-operator/runs/end-to-end-tests/5b9fa7f6c81a8a00066d8a96?step=5b9fa81e82df1e00070eb386) [[2]](https://app.wercker.com/Oracle/mysql-operator/runs/end-to-end-tests/5b9fa62a8c38a200070e28c3?step=5b9fa640f07af00007e89b6d)