script option: fix IndentationError with buildout 2, if some lines are indented.

slapos/recipe/build/__init__.py

@@ -28,6 +28,7 @@ import errno
 import logging
 import os
 from platform import uname
+import re
 import setuptools
 import shlex
 import shutil
@@ -271,8 +272,12 @@ class Script(EnvironMixin):
     for k in 'url', 'md5sum', 'path':
       self.options[k] = self.options.get(k, '').strip()
     self.script = self.options['script']
-    if self.options.get('format', 'yes') in TRUE_LIST:
+    if self.script:
+      if self.options.get('format', 'yes') in TRUE_LIST:
         self.script = self.script % self.options
+      if re.match(r'^\s', self.script):
+        # Buildout 2 keeps all indentation unless all lines have the same indentation.
+        self.script = 'if True:\n' + self.script
     if self.options.get('keep-on-error', '').strip().lower() in TRUE_LIST:
       self.logger.debug('Keeping directories in case of errors')
       self.keep_on_error = True