Looks like I solved the problem by getting some old code from the git repo, tagging it on local and building. Now it works under 2.1. However new problems came to surface. I will create a new topic for those.
In case somebody is wondering , the git SHA for the snaps I used is : dafcf0c861e552baf6f11d8a88c2df53bf32ee6d
in 91b182b265ba5432070f388cde04db149d39a162 I see the org.eclipse.virgo.kernel and related upgraded to 2.2.0.M01 in the "build.versions" file, so I decided that would take me over the edge. Am I wrong ? Should that still work on 2.1 ?