Don't use the default boot image location with non-default bootclasspath am: 6023b3a53a am: 450b61859e am: b34a8b2baa

Original change: https://android-review.googlesource.com/c/platform/art/+/2463234

Change-Id: Ie623099c48d8205d334dfa078650a160f5dfd246
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>