Pull duplicated report naming code into base class

We duplicated code to name report nodes in each class. However, each
name followed the same pattern, so we now abstract this pattern away
into the base class. Thereby, the child classes get simpler, and we're
prepared if we want to add extra information to the repr.

Change-Id: I7f412fe131fb36cfa45eb8361c8f87576342b36f