Change date on CustomCalendar

The date of the calendar is set by converting the epoch time based on
the local time zone. We choose at date at 12:00 GMT so that it will
be on the same day no matter which time zone is considered.

Test: part of testActivity
Change-Id: Ib36a5b45f69323265dd5ceaa17eeac553fc2d071
(cherry picked from commit 896cc3a794bb6e173c1e53e97f70007c3e24de38)