Add missing docstrings and don't copy generated payloads if only pre-generating.

devserver.py

Index: devserver.py
diff --git a/devserver.py b/devserver.py
index 7d4162d9475e919273f721dcc90b60e5a3bc449b..dc670af71b57f68106e9eddc867e11af2d8c64bc 100755
--- a/devserver.py
+++ b/devserver.py
@@ -193,7 +193,8 @@ if __name__ == '__main__':
       proxy_port=options.proxy_port,
       src_image=options.src_image,
       vm=options.vm,
-      board=options.board)
+      board=options.board,
+      copy_to_static_root=not options.exit)
 
   # Sanity-check for use of validate_factory_config.
   if not options.factory_config and options.validate_factory_config: