Ramp android-marshmallow-arm64-rel to 10% luci.

Formerly known as android_n5x_swarming_rel.

Bug: 731985
Change-Id: Iff1fa5c6cc6c0af2c9f995a53d921fe73eafa356
Reviewed-on: https://chromium-review.googlesource.com/1068254
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: John Budorick <jbudorick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560466}

infra/config/branch/cq.cfg

@@ -76,7 +76,11 @@ verifiers {
       name: "master.tryserver.chromium.android"
       builders {
         name: "android_n5x_swarming_rel"
-        equivalent_to { bucket: "luci.chromium.try" percentage: 0 }
+        equivalent_to {
+          bucket: "luci.chromium.try"
+          builder: "android-marshmallow-arm64-rel"
+          percentage: 10
+        }
       }
       builders {
         name: "cast_shell_android"