Comment 8 for bug 1461181

I think this can be fixed without the monkey patching with:
--- src/maasserver/bootresources.py 2015-06-02 08:46:21 +0000
+++ src/maasserver/bootresources.py 2015-06-27 01:17:41 +0000
@@ -666,6 +666,7 @@
                 cksummer.update(buf)
                 if len(buf) != self.read_size:
                     break
+ reader.close()

         if not cksummer.check():
             # Calculated sha256 hash from the data does not match, what