Turn off uploading of hwtest artifacts for Chromium builders.
Turn off uploading of hwtest artifacts for Chromium builders.

This can be turned back on once the dev server has implemented
appropriate locking.

TEST=cbuildbot_config_unittest.py
BUG=chromium-os:34768, chromium-os:32290

Change-Id: I406d6c945134cab8d4257dc0019921bf72ad8715
Reviewed-on: https://gerrit.chromium.org/gerrit/34208
Tested-by: David James <f231dc574bbeb62604660cbc162d1b8642a0a3af@chromium.org>
Reviewed-by: Don Garrett <546ec366615570e68497e3c5df9092106a9808f4@chromium.org>

chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,coreos/chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,chadversary/chromiumos.chromite,bpsinc-native/src_third_party_chromite,zhang0137/chromite,coreos/chromite,zhang0137/chromite,coreos/chromite