Fix test: configurations is accessible as instance method anymore in 4.1+
Fix order of assertions
Fix subclass verification of inheritance column with protected attrs

After rails/rails@8a60f479b0580e88bae77c0ab3dd9e95082cb437, the
implementation that builds the subclass based on the inheritance column
attribute has changed to fix a bug, and the method name followed this
change.

This updates the method name to match Rails current implementation in
branches 4-0, 4-1 and master.