Standarize image by using shared / similair layers

core/admin/Dockerfile

@@ -1,12 +1,16 @@
-FROM python:3-alpine
-
+FROM alpine:3.8
+# python3 shared with most images
+RUN apk add --no-cache \
+    python3 py3-pip \
+  && pip3 install --upgrade pip
+# Image specific layers under this line
 RUN mkdir -p /app
 WORKDIR /app
 
 COPY requirements-prod.txt requirements.txt
 RUN apk add --no-cache openssl curl \
- && apk add --no-cache --virtual build-dep openssl-dev libffi-dev python-dev build-base \
- && pip install -r requirements.txt \
+ && apk add --no-cache --virtual build-dep openssl-dev libffi-dev python3-dev build-base \
+ && pip3 install -r requirements.txt \
  && apk del --no-cache build-dep
 
 COPY mailu ./mailu