Fix exit status of ART script tools/teardown-buildbot-device.sh.

Simplify the logic deleting property_context files from the
chroot and prevent it from making the script return a non-zero
exit status.

Test: sh -x art/tools/teardown-buildbot-device.sh; echo $?
Bug: 34729697
Change-Id: Ia9f34eda2c167b26a6396937c7c4ecec01c86718
1 file changed