Add indicator example and callback function before/after test case running

Add a callback function before test case starts to run.
Add a callback function when test case completed.
indicator.py is a simple example to show how to add an indicator into
test_list

BUG=chrome-os-partner:23520
TEST=manually test

Change-Id: Ie826b7ed74419b65b56f9ec7b188a6692069cade
Reviewed-on: https://chromium-review.googlesource.com/175252
Reviewed-by: Heng-ruey Hsu <henryhsu@chromium.org>
Commit-Queue: Heng-ruey Hsu <henryhsu@chromium.org>
Tested-by: Heng-ruey Hsu <henryhsu@chromium.org>
3 files changed