Adds order to the test models to make the results more predictable.

Even though there was some code in place to prevent results in random
order from PostgreSQL we were still experiencing this with Jenkins
and Travis.

This commit removes the old code that handled this. From now on this
will be handled differently. Every test model will order by its
primary key. You can disable this by changing the order property
of the model to `null`: `$testModel->order = null`.
Merge pull request #1440 from Phally/master-postgres-fails

Adds order to the test models to make the results more predictable.