Add condition to check if a user can have profile user

- In Auto, headless system user is used, instead of split system user.
- When a profile user is being created based on a normal user, the normal
user should not be a system user if headless system user is enabled.
- We could consider defining isHeadlessSystemUser in UserManager.

Bug: 137195727
Test: Creating profile user in Android Auto should work in hawk_md
environment.

Change-Id: I47192d8f92320296d4220ded285a36b376e6d971