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Add mb configs and test configs for chromeos-betty-pi-arc-google-rel and its
optional trybot chromeos-betty-pi-arc-chrome

R=bpastene@chromium.org

Bug: 1000513
Change-Id: I7e64bd4c547b764ce5f5344711bff7232e941bc1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1788302Reviewed-by: Ben Pastene <bpastene@chromium.org>
Commit-Queue: Anushruth  <anushruth@chromium.org>
Cr-Commit-Position: refs/heads/master@{#696861}