Add libffi to all Postorius images. (#320)

* Add libffi to all Postorius images.

* Use Django less than a certain version.

* Fix the version constraint.

* Fix uwsgi configuration by using only processes.

postorius/Dockerfile.dev

@@ -16,8 +16,8 @@ ARG CLIENT_REF
 # rights for management script
 RUN set -ex \
 	&& apk add --no-cache --virtual .build-deps gcc libc-dev linux-headers git \
-	   	postgresql-dev mariadb-dev \
-	&& apk add --no-cache --virtual .mailman-rundeps bash \
+	   	postgresql-dev mariadb-dev libffi-dev \
+	&& apk add --no-cache --virtual .mailman-rundeps bash libffi \
 	   postgresql-client mysql-client py-mysqldb curl mailcap \
 	&& pip install -U git+https://gitlab.com/mailman/mailmanclient@${CLIENT_REF} \
 		                git+https://gitlab.com/mailman/postorius@${POSTORIUS_REF} \
@@ -26,7 +26,7 @@ RUN set -ex \
 		                psycopg2 \
 		                dj-database-url \
 		                mysqlclient \
-	&& pip install -U django==2.1.5\
+	&& pip install -U 'Django<2.2' \
 	&& pip install -U git+https://gitlab.com/mailman/django-mailman3@${DJ_MM3_REF} \
 	&& apk del .build-deps \
 	&& addgroup -S mailman \