Use one env var for DB connections

[rafaelespinoza]

what

Update the drivers to use one environment variable (DB_DSN) to connect to the DB.

why

The current way that DB connection strings are formed is pretty inflexible. It makes assumptions about how the DB is set up on the host system. For instance, it may be easier to not require ssl if it's a CI or development environment. The DB may connect over a socket instead of a TCP connection.

Also, it's a lot easier to manage one environment variable, rather than 5 (DB_HOST, DB_NAME, etc).

[rafaelespinoza]

Fixed in 1dc54d9