- order sections similar to sample configs
- add warnings and comments to `bootstrap.dcs` section.
- add `tags` and `log` sections.
- use discovered IPs in `postgresql.connect_address` and `postgresql.listen`
- set `wal_level` to `replica` for PostgreSQL 9.6+
- make unit tests pass with python 3.6
- improve config validator so it doesn't complain when some ints are strings in YAML file.