ART: Refactor run-test 924

Move testing to a dedicated thread to have a known thread name.
Change event reporting to be Java-side. Use Java-side thread list
(from Thread.getAllStackTraces) as comparison for minimal expected
set of threads.

Bug: 32072923
Test: art/test/testrunner/testrunner.py -b --host -t 924
Change-Id: I238ffc202e42eea8d1788137715188d3dfbcc8fb
3 files changed