This used to work due to side effects.
`rake parallel:migrate` used to work very inconsistently and would only migrate
some of the databases.
This introduces the recommended change to db.yml so the correct database is
found based off TEST_ENV_NUMBER if for some reason we did not set it using
RAILS_DB
Also avoids a bunch of schema dumping which is not needed when migrating
parallel specs
DB number 1 is very odd cause for whatever reason parallel spec is not
setting it.
