Use ApplicationRecord instead of ActiveRecord::Base
Because Rails 5 will require apps to use ApplicationRecord and because this makes things easier for us to redirect orchestration log messages from sql to orch logger, we are making a change in core and introducing this class (#13772).
Most ActiveRecord::Base use must be replaced, specifically:
app/model/ - model classes
db/migrate/ - "fake" reopened classes otherwise TypeError: superclass mismatch for class XYZ
test/ - reopened classes otherwise TypeError: superclass mismatch for class XYZ
Such an example change can be seen in https://github.com/theforeman/foreman/pull/3729