test_runner.py: Fix --wait-for-java-debugger when no under_test apk exists

Bug: 841628
Change-Id: I8bc446018bb19d6218c07f397fe96650e0a4ea4a
Reviewed-on: https://chromium-review.googlesource.com/c/1322353Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: agrieve <agrieve@chromium.org>
Cr-Commit-Position: refs/heads/master@{#606102}

build/android/pylib/local/device/local_device_instrumentation_test_run.py

@@ -298,9 +298,10 @@ class LocalDeviceInstrumentationTestRun(
         individual_device_set_up,
         self._test_instance.GetDataDependencies())
     if self._test_instance.wait_for_java_debugger:
+      apk = self._test_instance.apk_under_test or self._test_instance.test_apk
       logging.warning('*' * 80)
       logging.warning('Waiting for debugger to attach to process: %s',
-                      self._test_instance.apk_under_test.GetPackageName())
+                      apk.GetPackageName())
       logging.warning('*' * 80)
 
   #override