CTest: more aggressive implementation of ctest_empty_binary_directory()

Make sure that CMakeCache.txt is the last file being removed since
the binary directory may be left in a state that is no longer
removable otherwise.

Also retry removal a couple of times which makes this more robust
on windows where file locks may temporarily prevent removal.

Source/CTest/cmCTestScriptHandler.h

@@ -135,6 +135,9 @@ private:
   // Add ctest command
   void AddCTestCommand(cmCTestCommand* command);
 
+  // Try to remove the binary directory once
+  static bool TryToRemoveBinaryDirectoryOnce(const std::string& directoryPath);
+
   std::vector<cmStdString> ConfigurationScripts;
   std::vector<bool> ScriptProcessScope;