Pim 1674

First example of relationship cutting for future MongoDB support: Completeness and Product

Bug fix: [no]
Feature addition: [no]
Backwards compatibility break: [yes] Kills the relation between Product and Completeness
Unit test passes: [yes]
Behat scenarios passes: [yes]
Checkstyle issues: [no]
ChangeLog updated: [yes]
Documentation PR: [N/A]
Fixes the following jira:
 - PIM-1674