distgit: Actually hardlink over the existing source at the old path

Without this, the file could exist at both the old and new path, taking
the space on the disk twice.

This forces a hardlink if the file already existed at the old path.

roles/distgit/files/dist-git-upload.cgi

@@ -179,14 +179,26 @@ def main():
     # Add the file to the old path, where fedpkg is currently looking for it
     if hash_type == "md5":
         old_dir = os.path.join(module_dir, filename, checksum)
+        old_path = os.path.join(old_dir, filename)
 
         try:
             os.makedirs(old_dir)
-            os.link(dest_file, os.path.join(old_dir, filename))
+
         except OSError as e:
             if e.errno != errno.EEXIST:
                 raise e
 
+        try:
+            os.link(dest_file, old_path)
+
+        except OSError as e:
+            if e.errno != errno.EEXIST:
+                raise e
+
+            # The file already existed at the old path, hardlink over it
+            os.unlink(old_path)
+            os.link(old_path)
+
     # Emit a fedmsg message.  Load the config to talk to the fedmsg-relay.
     try:
         config = fedmsg.config.load_config([], None)