Return more informative errors from request/node

This makes the messages emitted by request/node on connection failure more informative.

Fixes https://github.com/theintern/leadfoot/issues/12
I didn't think of it. Also, the leadfoot expression will redact everything before an @ in a url, so something like `http://www.somewhere.com/something@home`, which is will end up as `http://redacted@home`.