Be more explicit about users

Be more explicit about users

Be more explicit about users executing processes in the time
zone updates code.The code was already running everything as the
system user but now that's more explicit / by design.

To service unit tests:
make -j30 FrameworksServicesTests
adb install -r -g "${ANDROID_PRODUCT_OUT}/data/app/FrameworksServicesTests/FrameworksServicesTests.apk"
adb shell am instrument -e package com.android.server.timezone -w com.android.frameworks.servicestests \
  "com.android.frameworks.servicestests/android.support.test.runner.AndroidJUnitRunner"

Bug: 64111659
Test: Unit tests: See above
Test: Manual testing installing updates as secondary device user
Test: PTS: run pts -m PtsTimeZoneTestCases
Change-Id: Idb754f3e1aa3830ba1ada8ef5740f9f7340f03d5
Merged-In: Idb754f3e1aa3830ba1ada8ef5740f9f7340f03d5
(cherry picked from commit 1281f39f86a8e4d9950581fb1f15245843856c23)