Error shown now when trying to create a new user with an existing email 

- Do not reactivate user in create action for this controller if provided email exists
- Instead, render again :new action to show errors
- Verified that this reactivate action is not the one used when reactivation a user from list of users option
- Created RSpec tests to:
  1. verify a user with empty email creates a dummy "user<id>@example.com" email 
  2. verify that if provided existing email we get error back