Use non-root user in Dockerfile

Signed-off-by: ecaiyanlinux <martin.c.yan@est.tech>
Issue-ID: NONRTRIC-656
Change-Id: Ib85abd9de806b30b73af34a863b06c7663026c3d
diff --git a/test/prodstub/Dockerfile b/test/prodstub/Dockerfile
index 4768bf9..0a027e4 100644
--- a/test/prodstub/Dockerfile
+++ b/test/prodstub/Dockerfile
@@ -32,4 +32,8 @@
 RUN apt-get update
 RUN apt-get install -y nginx=1.14.*
 
+RUN groupadd -g 999 appuser && \
+    useradd -r -u 999 -g appuser appuser
+USER appuser
+
 CMD [ "./start.sh" ]