ART: Relax failure requirements for dex2oat watchdog test

The watchdog does not clean up any output. It is theoretically
possible (though it should be very unlikely) that with the test
configuration the dex2oat run finishes writing the output before
the watchdog kills dex2oat.

Bug: 63052624
Test: m test-art-host-gtest-dex2oat_test
Change-Id: If5fc8936e18af8219f70de6f01c2ae7a993663a3