Add top level cloudbuild config to support multiple cloudbuild.yaml in cos/tools

BUG=b/183724535,b/183723138

Change-Id: I878892becce670a3ad10c5c7f0ff9825e6eec866
Reviewed-on: https://cos-review.googlesource.com/c/cos/tools/+/16110
Cloud-Build: GCB Service account <228075978874@cloudbuild.gserviceaccount.com>
Reviewed-by: Robert Kolchmeyer <rkolchmeyer@google.com>
Tested-by: Arnav Kansal <rnv@google.com>
diff --git a/cloudbuild.yaml b/cloudbuild.yaml
new file mode 100644
index 0000000..bd839e9
--- /dev/null
+++ b/cloudbuild.yaml
@@ -0,0 +1,19 @@
+steps:
+- name: 'gcr.io/cloud-builders/gcloud'
+  entrypoint: 'bash'
+  args:
+  - '-c'
+  - |
+    for d in src/cmd/*/; do
+      config="${d}cloudbuild.yaml"
+      if [[ ! -f "${config}" ]]; then
+        continue
+      fi
+
+      echo "Building $d ... "
+      (
+        gcloud builds submit $d --config=${config}
+      ) &
+    done
+    wait
+timeout: 3600s