Fix execution with RI in ART `testrunner.py` script.

Before this change, when the `art/test/testrunner/testrunner.py`
script was invoked only with option `--jvm`, no test would be run.

Test: art/test/testrunner/testrunner.py --jvm
Bug: 129406631
Change-Id: I92c85f5131d547fa9e3c6c47c82aa533a62a3f3e
1 file changed