Fix zipapex test-bot.

In the configuration used by the go/ab timeout_dumper will not be on
the path when running in the zipapex configuration. This changes the
run-test-jar to no longer rely on it being there for bionic targets.

Test: ./art/test/testrunner/run_build_test_target.py -j50 art-linux-bionic-x64-zipapex
Change-Id: I9e2867281058e392eb299982aea6c6619ac82bf5