Fix: autopkgtest now returns content-length header again

reverts commit 25eb52aa33

This must be reverted so that britney is aware of short reads of the db.

britney2/policies/autopkgtest.py

@@ -181,8 +181,7 @@ class AutopkgtestPolicy(BasePolicy):
                         if not data:
                             break
                         f_out.write(data)
-                content_length = f.getheader('content-length')
-                if http_code and content_length and os.path.getsize(new_file) != content_length:
+                if http_code and os.path.getsize(new_file) != int(f.getheader('content-length')):
                     self.logger.info('Short read downloading autopkgtest results')
                     os.unlink(new_file)
                 else: