ART: Call ThreadGroup.add for attached threads

When attaching threads to the runtime, call ThreadGroup.add to
let the thread's group know that the thread is now started. This
fixes incorrect internal accounting.

Test: art/test/testrunner/testrunner.py -b --host -t 169
Test: m test-art-host
Change-Id: I60362b6b53acf06b97779ea9b3b0bc6264f1dc2d
10 files changed