[autotest] test_that handles -i/--build option.

Provision the DUT to the requested build specified by -i/--build.
If provisioning fails, it will not run the tests.

TEST=1) Run with -i option, confirm that the DUT is successfully
provisioned.
2) Run without -i/--board option, confirm that the script still works.
3) Pass in an invalid value for -i, confirm that the script fails
without continuing to run the tests.
4) Confirm that sigint is still handled properly.
5) test_that_unittest passes
BUG=chromium:265713

Change-Id: I0a002a55127b3af4c6949934ce67f54c454e0a94
Reviewed-on: https://chromium-review.googlesource.com/169833
Reviewed-by: Fang Deng <fdeng@chromium.org>
Commit-Queue: Fang Deng <fdeng@chromium.org>
Tested-by: Fang Deng <fdeng@chromium.org>
2 files changed