Implemnet update_script support.

slapos/recipe/build.py

@@ -226,6 +226,7 @@ class Script:
     return True
 
   script = 'raise NotImplementedError'
+  update_script = None
 
   def __init__(self, buildout, name, options):
     self.cleanup_dir_list = []
@@ -294,8 +295,16 @@ class Script:
     return [self.options['location']]
 
   def update(self):
-    pass
-
+    if self.update_script is None:
+      return None
+    try:
+      env = self.getEnvironment()
+      exec self.options['update_script']
+    finally:
+      for d in self.cleanup_dir_list:
+        if os.path.exists(d):
+          self.logger.debug('Cleanup directory %r' % d)
+          shutil.rmtree(d)
 
 class Cmmi(Script):
   """Simple configure-make-make-insall compatible with hexagonit.recipe.cmmi