text: Title: Add an impersonation test case to the audit E2E test
  Body: We don't currently have any test coverage of impersonation for audit logging. I think the audit e2e test (https://github.com/kubernetes/kubernetes/blob/master/test/e2e/auth/audit.go) would be a good place to do so.
  
  /area audit
  /area test
  /sig auth
  /help
  /good-first-issue