Update work challenge header in Settings

* If organization name has been set for
  a managed profile, work challenge
  should display it as the header.

Bug: 155274026
Test: manual testing

Manual Testing Steps
* Set up device with managed profile
* Set organization name via TestDPC
* Go Settings > Security > Work profile security
  and add a work profile lock
* Select 'Work profile lock' and verify
  organization name is shown in header

Change-Id: I83209383fd2cf9179c34ccfdf8c097c379ec933e