rPuppy: Update Makefile and Dockerfile

Change-Id: I3832c88878b517554ceecaa89fe8a0a03ee1876f
diff --git a/apps/rpuppy/Dockerfile b/apps/rpuppy/Dockerfile
index 5b5f85e..0e425c5 100644
--- a/apps/rpuppy/Dockerfile
+++ b/apps/rpuppy/Dockerfile
@@ -1,6 +1,5 @@
-FROM alpine:latest
+FROM gcr.io/distroless/static:nonroot
 
 ARG TARGETARCH
 
 COPY rpuppy_${TARGETARCH} /usr/bin/rpuppy
-RUN chmod +x /usr/bin/rpuppy