Clarify that is_shared in practice gives access to system libs for am: 81b3f56cab am: 920ec80154 am: 01e7e9ce7c

Original change: https://android-review.googlesource.com/c/platform/art/+/2214689

Change-Id: I6e83fa4a56d39acffcdd3ead50fb04b7735dc890
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>