There are two questions,

1. Why is the odl-clustering-test-app part of the restconf feature set?
2. Why should odl-restconf-all contain odl-clustering-test-app?

The answer to (2) apparently is that the *-all feature set contains all the features in a feature set. The problem with (2) however is that inadvertently people who install tyhe odl-restconf-all feature set get clustering even though they did not specifically want it. Furthermore the clustering configuration files that come with odl-clustering-test-app require a 3 node cluster which results in a non-working cluster when other nodes of the cluster are not running.