Correct timeout_dumper to TIMEOUT_DUMPER

On linux_bionic-zipapex we don't have $ANDROID_HOST_OUT or
soong/host/linux_bionic-x86/bin on the PATH and timeout_dumper isn't
in the apex so we need to give its full path.

Test: ./art/test/testrunner/run_build_test_target.py -j50 art-linux-bionic-x64-zipapex
Change-Id: I33327e4d3ec4a23bf32dffaa61bfc30e04804405