Add test_that launching script to path

Add a script that launches autotest source tree's copy
of test_that to the chroot path.

CQ-DEPEND=CL:Iaeb425cb5575ceb67f868d3c8d8343a58255cae8

BUG=chromium:236471
TEST=If source tree test_that.py does not exist, script errors out with
appropriate message. Otherwise, test_that.py is launched and command
line args are passed along correctly.

Change-Id: I940e09d6986fe049eb4c94a91e3e484aabccd7a4
Reviewed-on: https://gerrit.chromium.org/gerrit/49496
Tested-by: Aviv Keshet <akeshet@chromium.org>
Reviewed-by: Chris Sosa <sosa@chromium.org>
Commit-Queue: Aviv Keshet <akeshet@chromium.org>
2 files changed