Have scrape time as a pseudovariable, not a prometheus variable.

This ensures it has the right timestamp, and is easier to work with.

Switch sd variable away from 'outcome', using total/failed instead.
Seems like this was wrong before, but our convention is to have separate import blocks (separated by empty lines) for:

- standard lib imports
- renamed standard lib imports
- third-party imports
- renamed third-party imports
- imports from same repo
- renamed imports from same repo

So `sync` should stay at the top, but have an empty line below it