cros_au_test_harness: Fix the issue with running vm/gce tests

CL:1808406 mistakenly removed the block to run the test if the
--parallel flag was not passed to the cros_au_test_harness (which we
don't pass it anyway). This CL puts that block back.

BUG=chromium:1006799, chromium:1006777
TEST=lakitu paladin tryjob
TEST= ./cros_au_test_harness.py -t \
      ~/chromiumos/images/chromiumos_test_image.bin \
      --test_prefix=SimpleTestVerify
Tried to run the test.

Exempt-From-Owner-Approval: achuit@ already +1'ed it.
Change-Id: Ib433b8b25bf3929b137e52e4ae97a47e21be1d2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crostestutils/+/1816809
Commit-Queue: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Sean Abraham <seanabraham@chromium.org>
Reviewed-by: Mike Frysinger <vapier@chromium.org>
2 files changed