Have tools/run-{libcore,jdwp}-tests.sh honor ART_TEST_CHROOT.

Also remove explicit handling of `--chroot` option from these
scripts.

Test: ART_TEST_CHROOT=/data/local/art-test-chroot tools/run-libcore-tests.sh --mode=device --variant=X64
Test: ART_TEST_CHROOT=/data/local/art-test-chroot tools/run-jdwp-tests.sh --mode=device --variant=X64
Bug: 34729697
Change-Id: Id583ea16b36c3eebc1f80868c06ed26174cb4533
2 files changed