ok, I have found that migrating existing ZenPacks from Zenoss 3.x to Zenoss 4.x need a few steps, but I'm not really sure about the correct way of doing this. What I have done is :
- remove EGG-INFO/
- write your ZenPacks.xxx.yyy/GNUmakefile
- write your ZenPacks.xxx.yyy/setup.py
- write your ZenPacks.xxx.yyy/ZenPacks/xxx/yyy/configure.zcml
The Zenpack installation (using ---link) works then, and you can start fixing up the other issues (modeler, skins, etc).