Minor improvements on UserInfoTest and UserManagerServiceUserInfoTest.

- Remove unnecessary AndroidJUnit4 runner
- Use Truth insteads of JUnit assertions
- Add @SuppressWarning (due to isPrimary() and FLAG_GUEST)
- Use withMessage() instead of just that()
- Use isTrue() / isFalse() instead of isEqualTo(boolean)
- Use expect instead of assert
- Consistenly use createTestUserInfo()
- Add missing assertions (like isSupervisingProfile())

Test: atest FrameworksCoreTests:UserInfoTest UserManagerServiceUserInfoTest
Bug: 374832167
Flag: TEST_ONLY

Change-Id: I5b4f89e24bb67656ccbd4447fee40f5078d39022