cpython3: use docker:cli image for kokoro instances docker image am: dc660d58db Original change: https://googleplex-android-review.googlesource.com/c/platform/external/python/cpython3/+/38356702 Change-Id: I6038be073b87965844bbea630db5c0ee3703e875 Signed-off-by: Automerger Merge Worker <[email protected]>