Force set timezone to UTC in logd.

(cherry picked from commit c27f12a3d396f113c5ae09d2f2c8ff7de3f8b551)

logd assumes that it is running in UTC time zone.
However, if persist.sys.timezone is set at some point later,
that affects and confuses logd behavior.
To avoid such a case, this CL sets TZ to UTC, which overrides
the property's behavior.

Test: Ran CtsOsTestCases.
Test: gTest liblog-unit-tests, logd-unit-tests and logcat-unit-tests
Bug: 33566779
Change-Id: Ib9edd4cb06f019a33aaf8d77d33bd82fdbbda480