Respect SYSTEM_EXT_ROOT in odrefresh am: 0a964610eb

Original change: https://android-review.googlesource.com/c/platform/art/+/2225897

Change-Id: I64d59ed53f610967493c87a9966bce72f692c13c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>