Back out "Fix speed change test to copy config at CB"

Summary:
setupconfigflag() is called before initAgent @ https://www.internalfb.com/code/fbsource/[9073b8e652ad23e5f47d8b58629146d6e9007c9c]/fbcode/fboss/agent/test/AgentTest.cpp?lines=52

And only in initAgent, Swswitch::Init is called which setups the bootype_ as warmboot or cold boot. Hence sw()->getBootType() will not be equal to Cold boot when checked inside setupconfigflag()

This causes speed change tests to fail. Backout and fix it using file check

Reviewed By: zechengh09

Differential Revision: D62063174

fbshipit-source-id: e86e2baa1bb3bb1f8cd92e9cbd7706cc0e2b6e6f

fboss/agent/test/link_tests/SpeedChangeTest.cpp

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