Feature repositories should aggregate (as opposed to redefine) single features.

This change request wants each single feature descriptor to define single feature while referencing dependency descriptors, but feature repository descriptor to define zero features and referencing single feature descriptors. This implies SingleFeatureTest will be run for every feature-related pom (but ending up testing nothing for the new feature repositories).

Basically, Karaf 3 feature-index [0] (from Integration/Distribution) is an example of what the generated feature repository should look like.

The main motivation is to speed up SingleFeatureTest and avoid duplicate definitions.

The fix probably requires changes to karaf-feature-plugin.

[0] https://nexus.opendaylight.org/content/repositories/opendaylight.release/org/opendaylight/integration/features-integration-index/0.5.2-Boron-SR2/features-integration-index-0.5.2-Boron-SR2-features.xml