Always perform quickmerge step when running test_that.

This scenario has come up multiple times. You are modifying your test
on your local machine but when you run test_that the code you added
isn't getting run. Test_that is running some other previous version
of your code.

You could chase down packages on the DUT or on your local box and look
for sentinel files or checksum files and delete them to trick test_that
to pickup your changes. Or, you can use a flag (--force) that
autotest_quickmerge.py' already supports.

Pass --force flag to autotest_quickmerge.py by default.

BUG=None.
TEST=I ran a local test. Will run test_that unit tests when I find out how to.

Change-Id: I0f8f6f3c6763defe45cb31ef64e815fbd75bc0ae
Reviewed-on: https://chromium-review.googlesource.com/264497
Tested-by: Mussa Kiroga <mussa@chromium.org>
Reviewed-by: Katherine Threlkeld <kathrelkeld@chromium.org>
Commit-Queue: Mussa Kiroga <mussa@chromium.org>
1 file changed