Fixes https://github.com/letsencrypt/boulder/issues/898
Also removes currently-unused 'development' DB, and do initial migrations in
parallel, which shortens create_db.sh from 20 seconds to 10 seconds.
Changes ResetTestDatabase into two functions, one each for SA and Policy DBs,
which take care of setting up the DB connection using a special higher-privileged
user called test_setup.
Jacob Hoffman-Andrews