Align system time 12-24 hour format in the time slot information

align the time format configuration in the Settings -> System ->
Date/Time to show 12- or 24- hour format in the usage time slot

screenshot: https://screenshot.googleplex.com/3w2SFvBLpC5oHBs
screenshot: https://screenshot.googleplex.com/86uCq6R4PKEg9RD
screenshot: https://screenshot.googleplex.com/3easrEFMQdZEjGP
screenshot: https://screenshot.googleplex.com/7dPWVJNTbSShFPa

Bug: 187783891
Test: make SettingsRoboTests
Change-Id: I9af0a69bd7c67562526bd5ee74a657635068ef44