What: As soon as a node passes the vetting criteria (total_audit_count and total_uptime_count
are greater than the configured thresholds), we set vetted_at to the current timestamp.
Why: We may want to use this timestamp in future development to select new vs vetted nodes.
It also allows flexibility in node vetting experiments and allows for better metrics around
vetting times.
Please describe the tests: satellitedb_test: TestUpdateStats and TestBatchUpdateStats make sure vetted_at is set appropriately
Please describe the performance impact: This change does add extra logic to BatchUpdateStats and UpdateStats and
commits another variable to the db (vetted_at), but this should be negligible.
Change-Id: I3de804549b5f1bc359da4935bc859758ceac261d
