PIM-3247: Can't display all variant groups on grid

* Improved behats
* updated CHANGELOG
* Fix bug on grid, variant groups were not correctly displayed. (max
result was applied to the joins and not directly on the variant group)
Merge pull request #1641 from akeneo/PIM-3247

PIM-3247: Can't display all variant groups on grid
Merge pull request #1642 from akeneo/1.2

1.2