This fixes an issue where multiple Grafana instances would race
to bootstrap the Grafana DB. The following changes are made:
- Only start additional Grafana instances after the DB has been
configured.
- During upgrade, don't allow old instances to run with an
upgraded DB schema.
Change-Id: I3e0e077ba6a6f43667df042eb593107418a06c39
Closes-Bug: #1888681