Qemu: Ensure ART_SSH_CMD is defined when running tests am: 5b2f97b131 am: b9f1d77781

Original change: https://android-review.googlesource.com/c/platform/art/+/2977711

Change-Id: Ice61a281f018f5b1891dab0860f1e01507cfcca7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>