PEP8 cleanup on node/backuptool.py through node/dht.py

The first of a few minor commits cleaning up style.  I'm trying to familiarize myself with the codebase while still being vaguely useful.
This one confuses me. I 'd like `key` and the `lamdba ...` part to appear as separate arguments, so please put them in different lines. Better yet, factor the lambda in a separate local function.