Move executor test setup code from TestT to TestMain

[unconsolable]

Enhancement

As currently tests under executor packages are using both pingcap/check and testify, we should move the test setup code in TestT to main_test.go to set up all of the tests written by both frameworks.

tidb/executor/executor_test.go

Lines 89 to 111 in 76267b2

	func TestT(t *testing.T) {
	CustomVerboseFlag = true
	*CustomParallelSuiteFlag = true
	logLevel := os.Getenv("log_level")
	err := logutil.InitLogger(logutil.NewLogConfig(logLevel, logutil.DefaultLogFormat, "", logutil.EmptyFileLogConfig, false))
	if err != nil {
	t.Fatal(err)
	}
	autoid.SetStep(5000)
	config.UpdateGlobal(func(conf *config.Config) {
	conf.Log.SlowThreshold = 30000 // 30s
	conf.TiKVClient.AsyncCommit.SafeWindow = 0
	conf.TiKVClient.AsyncCommit.AllowedClockDrift = 0
	})
	tikv.EnableFailpoints()
	tmpDir := config.GetGlobalConfig().TempStoragePath
	_ = os.RemoveAll(tmpDir) // clean the uncleared temp file during the last run.
	_ = os.MkdirAll(tmpDir, 0755)
	testleak.BeforeTest()
	TestingT(t)
	testleak.AfterTestT(t)()
	}

From my point of view, code related to pingcap/check can still be here, while code related to testleak can be replaced by goleak enabled in TestMain. All the other code will be better to move to TestMain.