enable flaky test to all tests

[hawkingrei]

Enhancement

We have many unstable tests in the tidb repo and we will create many unstable tests the everyday. In history, we put more attention on fixing the unstable test. and we find many unstable tests due to the bad design of test cases. All of us feel upset and take more time to wait to fixing the unstable test and speed more money to bug more machines to fight the unstable tests. we need to change our minds. we should retry unstable tests and report them to the dashboard. then to make the people fix the unstable test to clear the dashboard.