* Change test suite to fit expected behaviour
This reverts some changes from ansible/ansible@723daf3
If a line is found in the file, exactly or via regexp matching, it must
not be added again.
insertafter/insertbefore options are used only when a line is to be
inserted, to specify where it must be added.
* Implement the change in behaviour mentioned in the previous commit
* Fix comment to reflect what the code does
* Set the correct return message.
In these cases, the lines are added, not replaced.
* Add a changelog
2fb9b46752