Use standard alpine image as base for mailman-web

This way we can depend on alpine's python3 package which is binary
compatible with the rest of the python packages in the distribution.

This requires spelling out python3 explicitly in several places since
alpine still defaults to python 2 for /usr/bin/python.

web/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.6-alpine3.7
+FROM alpine:3.8
 
 MAINTAINER Abhilash Raj
 
@@ -12,11 +12,12 @@ COPY docker-entrypoint.sh /usr/local/bin/
 # rights for management script
 RUN set -ex \
 	&& apk add --no-cache --virtual .build-deps gcc libc-dev linux-headers \
-	   	postgresql-dev mariadb-dev \
+		postgresql-dev mariadb-dev python3-dev \
 	&& apk add --no-cache --virtual .mailman-rundeps bash sassc \
 	   postgresql-client mysql-client py-mysqldb curl mailcap \
-	&& pip install -U django==2.1.5 pip \
-	&& pip install mailmanclient==3.2.1 \
+	   python3 py3-setuptools \
+	&& python3 -m pip install -U django==2.1.5 pip \
+	&& python3 -m pip install mailmanclient==3.2.1 \
 		postorius==1.2.2 \
 		hyperkitty==1.2.1 \
 		django-mailman3==1.2.0 \
@@ -43,3 +44,5 @@ STOPSIGNAL SIGINT
 
 ENTRYPOINT ["docker-entrypoint.sh"]
 CMD ["uwsgi", "--ini", "/opt/mailman-web/uwsgi.ini"]
+
+ENV PYTHONPATH=/usr/lib/python3.6/site-packages

web/docker-entrypoint.sh

@@ -16,7 +16,7 @@ function wait_for_postgres () {
 
 function wait_for_mysql () {
 	# Check if MySQL is up and accepting connections.
-	HOSTNAME=$(python <<EOF
+	HOSTNAME=$(python3 <<EOF
 try:
     from urllib.parse import urlparse
 except ImportError:
@@ -112,11 +112,11 @@ else
 fi
 
 # Collect static for the django installation.
-python manage.py collectstatic --noinput
+python3 manage.py collectstatic --noinput
 
 # Migrate all the data to the database if this is a new installation, otherwise
 # this command will upgrade the database.
-python manage.py migrate
+python3 manage.py migrate
 
 # If MAILMAN_ADMIN_USER and MAILMAN_ADMIN_EMAIL is defined create a new
 # superuser for Django. There is no password setup so it can't login yet unless
@@ -124,7 +124,7 @@ python manage.py migrate
 if [[ -v MAILMAN_ADMIN_USER ]] && [[ -v MAILMAN_ADMIN_EMAIL ]];
 then
 	echo "Creating admin user $MAILMAN_ADMIN_USER ..."
-	python manage.py createsuperuser --noinput --username "$MAILMAN_ADMIN_USER"\
+	python3 manage.py createsuperuser --noinput --username "$MAILMAN_ADMIN_USER"\
 		   --email "$MAILMAN_ADMIN_EMAIL" 2> /dev/null || \
 		echo "Superuser $MAILMAN_ADMIN_USER already exists"
 fi
@@ -134,7 +134,7 @@ fi
 if [[ -v SERVE_FROM_DOMAIN ]];
 then
 	echo "Setting $SERVE_FROM_DOMAIN as the default domain ..."
-	python manage.py shell -c \
+	python3 manage.py shell -c \
 	"from django.contrib.sites.models import Site; Site.objects.filter(domain='example.com').update(domain='$SERVE_FROM_DOMAIN', name='$SERVE_FROM_DOMAIN')"
 fi
 

web/mailman-web/manage.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 import os
 import sys