Bump python version to 3.9 to address several vulnerability problems
FYI, I made these changes with the goal of addressing the issues shown in the vulnerability scan of the Docker image because, as per Amol's input, the vulnerabilities were related to libraries used in the python Docker image
Additionally, I removed some of the packages from the requirements file because they are already installed when Flask get installed because they are Flask's dependencies. Moreover, `dataclasses` got integrated into Python in version 3.7
Change-Id: I41fdfbde37cecb59bcdc728692ae33bd40a487e9
diff --git a/docker/Dockerfile b/docker/Dockerfile
index 39e3e97..3f2c182 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -3,7 +3,7 @@
# SPDX-FileCopyrightText: 2020-present Open Networking Foundation <info@opennetworking.org>
# SPDX-License-Identifier: Apache-2.0
#
-FROM python:3.6-slim-buster
+FROM python:3.9-slim-buster
RUN useradd -ms /bin/bash ubuntu
USER ubuntu