proper cleanup onDestroy

1. interrupt the sleeping testing thread onDestory to avoid
any thread keep running after onDestory.
2. add check of isFinishing() or isDestoryed() when the
testing thread wakeup.
3. detory the webview onDestory since there're chances that
some callbacks in WebChromeClient will try to open dialogs
while the container activity has been destroyed.

Bug: 63819703
Test: Manual test
Change-Id: Ida62d9d8e97e8c9f905ce2feab4ea265575baee8