SERVER-104276 added a wait for replication before attempting to step up the secondary in this test. However, this can still fail, seemingly if the primary steps down in response to the vote request which generates some writes (reasoning taken from this comment). To avoid this, we need some retry loop for the step up, but it looks as though the replsettest actually implements a stepUp function including the necessary waits and retries, so instead of writing this again ourselves, we should rely on this helper.