ensure environment is run before db:structure:load

Right now `db:drop` depends on `load_config` since so when `db:drop` gets executed `load_config` gets run. `db:structure:load` depends on `[:environment, :load_config]`. So before it runs, it executes `environment` but because `load_config` has already executed it is skipped. Note `db:load_config` is "invoke"-d twice, but only "execute"-d once:

```
** Invoke db:drop (first_time)
** Invoke db:load_config (first_time)
** Execute db:load_config
** Execute db:drop
** Invoke db:structure:load (first_time)
** Invoke environment (first_time)
** Execute environment
** Invoke db:load_config
** Execute db:structure:load
```

The fix for this is making sure that the environment is run before any `load_config`:

```
** Invoke environment (first_time)
** Execute environment
** Invoke db:drop (first_time)
** Invoke db:load_config (first_time)
** Execute db:load_config
** Execute db:drop
** Invoke db:structure:load (first_time)
** Invoke environment
** Invoke db:load_config
** Execute db:structure:load
```

railties/test/application/rake/dbs_test.rb

@@ -129,7 +129,7 @@ module ApplicationTests
            bundle exec rake db:migrate db:structure:dump`
           structure_dump = File.read("db/structure.sql")
           assert_match(/CREATE TABLE \"books\"/, structure_dump)
-          `bundle exec rake db:drop db:structure:load`
+          `bundle exec rake environment db:drop db:structure:load`
           assert_match(/#{expected[:database]}/,
                         ActiveRecord::Base.connection_config[:database])
           require "#{app_path}/app/models/book"