Fix speed change test to copy config at CB

Summary:
As titled. If the old config is preserved on the box, it will not get updated and hence the test keep running with old config.

This has caused link tests failing on conveyor with old config preserved. Fixing this by explicitly checking cb

Differential Revision: D62006182

fbshipit-source-id: 2a394242a0e5d36dd75d4d99c2ec1df42b167d77

fboss/agent/test/link_tests/SpeedChangeTest.cpp

@@ -206,9 +206,8 @@ void SpeedChangeTest::setupConfigFlag() {
   originalConfigCopy =
       linkTestDir + "/agent_speed_change_test_original_config.conf";
 
-  // Create a copy of the original config if we haven't created one before.
-  if (!boost::filesystem::exists(originalConfigCopy)) {
-    // Likely a coldboot iteration
+  // Create a copy of the original config during coldboot
+  if (sw()->getBootType() == BootType::COLD_BOOT) {
     utilCreateDir(linkTestDir);
     boost::filesystem::copy_file(FLAGS_config, originalConfigCopy);
   }