Update references to the ART APEX for tests.

Test: art/tools/buildbot-build.sh --host && art/test.py --host --64 --optimizing
Test: art/tools/run-gtests.sh in chroot
  (fails on instruction_set_features_test, but that's not related to this
  change - filed b/139425971)
Test: art/test/testrunner/testrunner.py --target --64 in chroot
Test: art/tools/run-libcore-tests.sh --mode=device --variant=X64 in chroot
Test: art/tools/run-jdwp-tests.sh --mode=device --variant=X64 in chroot
Bug: 135753770
Change-Id: I876c5a2931970d6a75c1812e0f87bc65ab7bde0f