recipe/promise_plugin: Add extra-paths option

slapos/recipe/promise_plugin.py

@@ -127,8 +127,18 @@ class Recipe(GenericBaseRecipe):
       for key in self.options
       if key.startswith('config-')}
 
+    sys_paths = [dist.location for dist in working_set]
+    extra_paths = self.options.get('extra-paths')
+    if extra_paths:
+      for p in extra_paths.splitlines():
+        p = p.strip()
+        if p:
+          if not os.path.isdir(p):
+            raise ValueError("Invalid extra path %s" % p)
+          sys_paths.append(p)
+
     return self.createFile(self.options['output'], script_template % {
-      'path': pformat([dist.location for dist in working_set], indent=2),
+      'path': pformat(sys_paths, indent=2),
       'content': content_string,
       'config': pformat(config_dict, indent=2),
       }, int(self.options.get('mode', '0644'), 8)),