Fix incorrect argument order in r221173.
Fix incorrect argument order in r221173.

Fix the way we pass --clusters to sharding_supervisor.py. This argument must
come after the test executable path, so that sharding_supervisor.py would pass
it on to run_test_cases.py instead of treating it as one of its own arguments.

BUG=283907
TBR=maruel@chromium.org

Review URL: https://chromiumcodereview.appspot.com/23444036

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@221180 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build