run-test build: Don't merge the shards by default. am: 720dcbc15b am: cf3a41ab08 am: 6c982ccefc

Original change: https://android-review.googlesource.com/c/platform/art/+/2273466

Change-Id: I2699cf189bef075e67bc9d484b7f5f1c859e8f92
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>