cloud build: use files from csi-release-tools

cmd/csi-snapshotter/Dockerfile

@@ -1,6 +1,7 @@
 FROM gcr.io/distroless/static:latest
 LABEL maintainers="Kubernetes Authors"
 LABEL description="CSI External Snapshotter Sidecar"
+ARG binary=./bin/csi-snapshotter
 
-COPY ./bin/csi-snapshotter csi-snapshotter
+COPY ${binary} csi-snapshotter
 ENTRYPOINT ["/csi-snapshotter"]

cmd/snapshot-controller/Dockerfile

@@ -1,6 +1,7 @@
 FROM gcr.io/distroless/static:latest
 LABEL maintainers="Kubernetes Authors"
 LABEL description="Snapshot Controller"
+ARG binary=./bin/snapshot-controller
 
-COPY ./bin/snapshot-controller snapshot-controller
+COPY ${binary} snapshot-controller
 ENTRYPOINT ["/snapshot-controller"]