Changes to support loading tz data from APEX

The changes needed to pick up time zone data files from
a mounted APEX directory. Code that looks for time zone
data now looks in a new location after checking for
data installed by the time zone updates via APK feature.

This hasn't been tested in combination with a real APEX but
it shouldn't do anything bad if the new path does not exist.

Bug: 115612964
Test: CTS: run cts-dev -m CtsBionicTests
Test: Build / boot without APEX support
Change-Id: I56ae50e26f2cbfa0e537029a0e6f679fa2394327