Do not import Download directly.

  This may cause an import chicken-egg problem, so this also reduce
  the amount of imports to be done.

slapos/recipe/cmmi/__init__.py

@@ -11,7 +11,6 @@ import shutil
 import subprocess
 import sys
 import zc.buildout
-from zc.buildout.download import Download
 try:
   # import from zc.buildout>2
   from zc.buildout.buildout import bool_option
@@ -172,7 +171,8 @@ class Recipe(object):
                 return self.buildout.get(platform_part)
 
     def download_file(self, url):
-        download = Download(self.buildout['buildout'], hash_name=True)
+        download = zc.buildout.download.Download(
+          self.buildout['buildout'], hash_name=True)
         url, _s_, md5sum = url.partition('#')
         return download(url, md5sum=md5sum or None)