storage: Fix semantics for directory size

The actual directory size is "used" space, not the total space on
the filesystem.

Signed-off-by: Michael Hanselmann <hansmi@google.com>
Reviewed-by: Iustin Pop <iustin@google.com>

lib/storage.py

@@ -102,7 +102,7 @@ class FileStorage(_Base):
     values = []
 
     # Pre-calculate information in case it's requested more than once
-    if COL_SIZE in fields:
+    if COL_USED in fields:
       dirsize = utils.CalculateDirectorySize(path)
     else:
       dirsize = None
@@ -116,7 +116,7 @@ class FileStorage(_Base):
       if field_name == COL_NAME:
         values.append(path)
 
-      elif field_name == COL_SIZE:
+      elif field_name == COL_USED:
         values.append(dirsize)
 
       elif field_name == COL_FREE: