file_contexts_asan

This CL changes the policy for ASAN files on-disk to support the
changes made by the following CLs -
https://android-review.googlesource.com/#/c/359087/
https://android-review.googlesource.com/#/c/359389/

which refactor the on-disk layout of sanitized libraries in the following
manner -
/data/lib* --> /data/asan/system/lib*
/data/vendor/* --> /data/asan/vendor/*

There are a couple of advantages to this, including better isolation
from other components, and more transparent linker renaming and
SELinux policies.

Bug: 36574794
Bug: 36674745
Test: m -j40 && SANITIZE_TARGET="address" m -j40 and the device
boots. All sanitized libraries are correctly located in /data/asan/*,
and have the right SELinux permissions.

Change-Id: Ib08e360cecc8d77754a768a9af0f7db35d6921a9