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

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

Change-Id: If6195c5ffb729e1835f4cef3d0b3ebf0e118fa34
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>