This allows to manage the versions of the correctness DB.
It's the analog to the perf_migratedb app.

This is a prerequisite to roll out correctness to production.

BUG=skia:2930

Review URL: https://codereview.chromium.org/694263002
Add DataHopper program for pushing data into InfluxDB

Adds several utility modules:
- Rietveld
- Git
- Gitiles
- AutoRoll

DataHopper initially just pushes the current AutoRoll status into InfluxDB.
It's possible that other AutoRoll-related metrics could be added, eg. time
between landing a commit and rolling it into Chromium.

BUG=skia:3036

Review URL: https://codereview.chromium.org/697873004