Ensure that the testlogger has its final test removal safely (#16907)

It is possible to get a data race right at the end of the TestMain
in integrations during the final removal of the test from the testlogger. This PR
uses a Reset function to remove any final tests but adds some extra
logging which will forcibly fail if there is an unclosed logger.

Signed-off-by: Andrew Thornton <art27@cantab.net>

integrations/integration_test.go

@@ -120,7 +120,7 @@ func TestMain(m *testing.M) {
 	}
 	exitCode := m.Run()
 
-	writerCloser.t = nil
+	writerCloser.Reset()
 
 	if err = util.RemoveAll(setting.Indexer.IssuePath); err != nil {
 		fmt.Printf("util.RemoveAll: %v\n", err)