Feature config files in non-standard locations

This Bug is mainly for Lithium, Beryllium was not examined yet.

Some projects do not place their config files in standard locations (etc/opendaylight/karaf/ or configuration/initial/).

Most notably Capwap, Coretutorials and Vpnservice only specify file names.
Sfc uses configuration/startup/ and Usc uses etc/usc/, which maybe is standard enough, or maybe not.

The standard locations can be defined in several ways. Some projects write etc/opendaylight/karaf/ directly in feature definitions, some put it in properties such as config.configfile.directory.

The best action would be to define a common property in odlparent (perhaps using ${karaf.etc}) and contribute changes to all projects (including archetypes) so they refer to this property.