Add test to verify Users settings shows in secondary user.

- also update launch sequence for Users settings tests as Users settings
has been moved inside system settings and the preference title has
changed.
- and change the test to run with AndroidJUnit4.

Change-Id: I049b83f9ae4b2724608af267e8900dd9e6749874
Fixes: 34774778
Test: make SettingsUnitTests