Fix the flaky test by using the system time zone

In different timezone, it may cause the date time result is not as
expected. Use the system time zone to fix the issue.

Test: atest DateTimeUtilsTest
Test: run test with the timezone and the time from issue
Fix: 194762210
Fix: 194762152
Fix: 194761559
Fix: 194761674
Fix: 194762151
Change-Id: Ic724607e42419d2654f80a6a211d5004bddf1464
1 file changed