Fix dob date validation on custom locale

[joachimVT]

Description

Validations not working on customer registration on DOB field when changing the default locale. This pull request fixed the javascript date validation.

Fixed Issues (if relevant)

1. Frontend: Datepicker/calendar control does not use the store locale #6350
2. Invalid date when customer validate with French locale #9743
3. DatePicker date format does not reflect user's locale #6858
4. Magento 2.1.1 Invalid input date format 'Invalid date' #6831
5. Validations not working on customer registration on DOB field.  #4248

Manual testing scenarios

1. Set Backoffice to Dutch locale : account settings ->language Dutch (Dutch)
2. Modify a customer and set date of birthday (for example : 24-11-1980)

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[nelero]

same problem with start/end date for catalog rule

[digvijay2017]

This issue still exists in Magento 2.2.1, while i have set Interface Locale UK from admin setting.