Add regression test for deadlock caused by Thread.getAllStackTraces

Also added stress test for Thread.getAllStackTraces. The test calls
Thread.getAllStackTraces from multiple threads to stress race
conditions which can cause deadlocks.

Bug: 18661622

Change-Id: Ideee7073fdcce784414808d08eca9ea310240073
Merge "Add regression test for deadlock caused by Thread.getAllStackTraces"