Process promises that don't modify processes should be kept, not repaired

Some uses of process promises do not modify the system in any way, e.g. they just set a class.
In this case the promise is flagged as repaired today (both class- and reporting-wise AFIK).

We should make them kept, ideally before 3.7.0beta (slight behaviour change although I don't believe people rely on this).

The reason this is important now is that it is a glaring problem in the new Changes UI (see attachment:ootb-hub-process-changes.png).

Minimum is that process: promises that only have restart_class (as process-specific attributes) are always flagged as kept.
Ideally all process promises are kept unless either of @signals@ or @process_stop@ is defined.