Update ThreadTest#test_isDaemon.

Threads must inherit their daemon-ness from their parents. The vogar
version of junit uses a thread pool executor with daemon threads to
run tests.

Also contains a minor cleanup to prevent a thread from "leaking" outside
a test method.

bug: 26415594
bug: 26326992
Change-Id: Id555cce44b8ba14a090a7a846e0bbbc9671ad6ef
1 file changed