Merge pull request #1690 from akeneo/PIM-3221

PIM-3221: Fix bug on variant group import
PIM-3283: Password reset does not work
Merge pull request #1692 from akeneo/PIM-3283

PIM-3283: Password reset does not work
PIM-3209: Fix import running even with wrong file

*Added verification of the file extention before the launch of the job
*Added new behats in order to verify that the file extention is allowed or not