Add boot.art.rel files to system image

This file is used to verify that all differences between /system
boot*.art and /data/dalvik-cache boot*.art only consist of relocation
changes. The goal is to mitigate /data/dalvik-cache boot*.art files
being a persistence vector.

Test: Build and ensure boot.art.rel files are on the image.
Bug: 66697305
Change-Id: I41486dd541e429f2f2b4c4a521009ee5e81e50b9