Primary artifact type must be coherent: not "pom" if "zip" for example

For now, if we look at nuxeo-distribution-dm, the primary (default) artifact has zip type in theory but its POM says "pom" packaging, so there are resolving issues and Nexus search don't show the primary artifact even if it shows the POM and the attached artifacts (with classifiers).
We need to specify a packaging type for our assemblies and correctly set this primary artifact (default build result without classifier) on the Maven project.

There are cases where zip artifacts are only classifiers and so attached to the artifact but there's no primary artifact. In those cases, the primary artifact will be the pom itself. For example: nuxeo-distribution-jboss.