Preload the string-escape code in noded

This encoding, part of the standard Python installation, is used by
the pickle module (in turn used by subprocess when handling
failures in program execution). Preloading it means that Python will
cache it in memory so that even if the disk goes away or just the
module, we're not going to fail in reporting errors.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>