Apply check for "Require Unique Email Address" on I-9 form

Environment - LB
Prerequisite - Set "Require Unique Email Address" from Company Information>System Settings to "Yes"

Steps:
1] Add a new employee so that he is eligible for OB tour having I-9 form in it.
2] Start navigating OB tour, on I-9 form in Email Address field add email address which is already exists.

Actual Result:
I-9 form get saved with duplicate email ID and same email id set as employee email on Demographics page as well.
Expected Result:
I-9 form should not accept duplicate email ID.
Please made this enhancement applicable for all other forms (like I-9), if above issue is reproduce with them as well.

Cc: Saurabh Sablaka, Prasad Pise