Bug #114: Product IUs are missing in update sites(Merge branch 'pu/114-add-products-to-update-sites' into next)

Conflicts:
	b2-model-builder/src/main/java/org/sourcepit/b2/directory/parser/internal/extensions/ProductExtender.java
	b2-model-builder/src/main/java/org/sourcepit/b2/internal/generator/ProductProjectGenerator.java
	b2-model-builder/src/test/java/org/sourcepit/b2/directory/parser/internal/extensions/ProductExtenderTest.java
	b2-model-builder/src/test/java/org/sourcepit/b2/internal/generator/ProductProjectGeneratorTest.java