Report actual disk size, not apparent size

nilmdb/utils/diskusage.py

@@ -21,7 +21,8 @@ def du(path):
     errors that might occur if we encounter broken symlinks or
     files in the process of being removed."""
     try:
-        size = os.path.getsize(path)
+        st = os.stat(path)
+        size = st.st_blocks * st.st_blksize
         if os.path.isdir(path):
             for thisfile in os.listdir(path):
                 filepath = os.path.join(path, thisfile)