Currently Cockroach isn't performant for concurrent database setup and
tear-down. Instead of a single instance allow setting multiple potential
connection strings and let the tests pick one connection string
randomly.
This improves test duration by ~10 minutes.
While we are at significantly changing how pgtest works, introduce
helper PickPostgres and PickCockroach for selecting the database to
reduce code duplications in multiple places.
Change-Id: I8ad171d5c4c8a4fc081ec2ae9bdd0cc948a80619
Replace all the remaining uses of sql.DB with tagsql.DB to
fix issues with context cancellation.
Introduce tagsql.Open which helps to get rid of all tagsql.Wrap-s.
Use tagsql in cockroachkv and postgreskv.
Change-Id: I8946d203341cb85a25976896fc7881e1f704e779
first, so that they all work the same way, because it's getting
complicated, and second, so that we can do the appropriate thing
instead of CREATE SCHEMA for cockroachdb.
Change-Id: I27fbaeeb6223a3e06d97bcf692a2d014b31465f7
