Fix rails_parallel on generate schema.

### Problem
Calling `invoke_task('db:create', :force)` will not work if create relies on other tasks.
If `db:create` calls another rake task, for instance, `db:create => "db_charmer:create"` , even if we force on the second time, it would not work as we have to force the parent too.

### Solution

To avoid this type of weird edge cases, we should not use force whatsoever. 

To sum-up my changes:
- I don't call `create` in the beginning anymore, as we can assume the DB exists if running parallel tests.
- Added a `load_config` call, because as we overwrite `ActiveRecord::Base.configurations` we cannot call `load_config` after, otherwise we will lose the values.
- Remove force on `drop` `create` `setup` as they are not necessary anymore.

quickly review
@boourns @camilo @hornairs