Rename ANDROID_RUNTIME_ROOT to ANDROID_ART_ROOT following APEX module name change.

Test: Build & boot
Test: art/tools/run-libcore-tests.sh --mode=device --variant=X64 in ART chroot test environment
Test: art/tools/run-libcore-tests.sh --mode=host
  (fails on org.apache.harmony.tests.java.lang.MathTest#test_cbrt_D, but seems unrelated:
  junit.framework.AssertionFailedError: expected:<3.0> but was:<3.0000000000000004>)
Bug: 135753770
Change-Id: Icfd23c0dc0a3d868dc519d8c28c9413ce37cfdb0
2 files changed