Fix: FileAlreadyExistsException during archive copy

src/main/java/com/sheepit/client/DirectoryManager.java

@@ -81,6 +81,7 @@ public class DirectoryManager {
 		}
 		
 		try {
+			Files.deleteIfExists(targetArchivePath);  // createLink only works if the target does not exist
 			try {
 				Files.createLink(targetArchivePath, existingArchivePath);
 				log.debug("Created hardlink from " + targetArchivePath + " to " + existingArchivePath);