Create /app/backup so AbstractOLT can start

Change-Id: I5ef181256282966b2e2a9848d8cf146e4fcb356e
diff --git a/Dockerfile b/Dockerfile
index 6016d9e..5ecb550 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -47,6 +47,7 @@
 WORKDIR /app
 COPY --from=builder /go/src/gerrit.opencord.org/abstract-olt/bin/AbstractOLT /app/AbstractOLT
 COPY --from=builder /go/src/gerrit.opencord.org/abstract-olt/bin/client /app/client
+RUN mkdir -p /app/backup
 
 EXPOSE 7777/tcp
 EXPOSE 7778/tcp