Treat system_ext as system container am: 01efb834

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/3261301



Change-Id: Ic6c35f5e647e8693a852f8528ff5758f5ae8693e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>