Plugins migrated to Karaf4 must have set packaging to: kar
Maven will generate also karaf archive including all features of the plugin. Problem is that the resulting karaf archive doesn't include features.xml file in its root as it is required by KarafFeatureLoader.
Seems that there's no way how to force creation of such karaf archives by maven so it will be probably needed to implement optional parameter for karaf archive install RPC where will be specified location of repository file (features.xml) in the karaf archive. It is located in one of directories in repository directory of the archive and it has different name consisting of artifact ID and version.

It's possible that there are still some other issues causing broken KarafFeatureLoader. They need to be investigated e.g. by some small (hello world) plugin.

We need to minimize number of dependencies of plugins so this task should be dependent on the task: https://bugs.opendaylight.org/show_bug.cgi?id=8282