Enable better db/structure.sql output

This allows views to be propagated to the db/structure.sql file and
also limits the extraneous PRIMARY_KEY=123123123123 noise we get
that pollutes commits to this file.

The tests can be run with:

```
mysql-u root -e 'create database activerecord_unittest'
mysql-u root -e 'create database activerecord_unittest2'
mysql -u root -e "create user 'rails'@'localhost'"
mysql -u root -e "grant all privileges on activerecord_unittest.* to 'rails'@'localhost'"
mysql -u root -e "grant all privileges on activerecord_unittest2.* to 'rails'@'localhost'"
ARCONN=mysql2 bundle exec ruby -I"lib:test" test/cases/connection_adapters/abstract_mysql_adapter_test.rb
```

The ability to pull in views is a requirement for reporting.