Updated the Dockerfile to switch to python 3.8

Dockerfile

@@ -4,6 +4,8 @@ FROM ubuntu:xenial as base
 
 # Install system requirements
 RUN apt-get update && \
+    apt-get install -y software-properties-common && \
+    apt-add-repository -y ppa:deadsnakes/ppa && apt-get update && \
     # Global requirements
     DEBIAN_FRONTEND=noninteractive apt-get install --yes \
     build-essential \
@@ -20,7 +22,6 @@ RUN apt-get update && \
     libxml2-dev \
     libxmlsec1-dev \
     libxslt1-dev \
-    software-properties-common \
     swig \
     # openedx requirements
     gettext \
@@ -39,19 +40,15 @@ RUN apt-get update && \
     libxslt1-dev \
     ntp \
     pkg-config \
-    python3-dev \
-    python3-pip \
-    python3.5 \
-    && rm -rf /var/lib/apt/lists/*
+    python3.8-dev \
+    python3.8-venv \
+    &&rm -rf /var/lib/apt/lists/*
 
 RUN locale-gen en_US.UTF-8
 ENV LANG en_US.UTF-8
 ENV LANGUAGE en_US:en
 ENV LC_ALL en_US.UTF-8
 
-RUN ln -s /usr/bin/pip3 /usr/bin/pip
-RUN ln -s /usr/bin/python3 /usr/bin/python
-
 WORKDIR /edx/app/edxapp/edx-platform
 
 ENV PATH /edx/app/edxapp/nodeenv/bin:${PATH}
@@ -61,8 +58,12 @@ ENV PATH /edx/app/edxapp/edx-platform/bin:${PATH}
 ENV SETTINGS production
 RUN mkdir -p /edx/etc/
 
+ENV VIRTUAL_ENV=/venv
+RUN python3.8 -m venv $VIRTUAL_ENV
+ENV PATH="$VIRTUAL_ENV/bin:$PATH"
+
 # Install Python requirements
-RUN pip install pip==20.0.2
+RUN pip install pip==20.2.3
 COPY setup.py setup.py
 COPY common common
 COPY openedx openedx