use our ubuntu base for certstrap + cf-acceptance-tests

certstrap/Dockerfile

@@ -1,9 +1,8 @@
-FROM ubuntu:20.04
+FROM ghcr.io/alphagov/paas/ubuntu:main
 
 ENV GIT_COMMIT bd8b02aa8c1b81bc5cfc070722a1a894a348f00a
 ENV CERTSTRAP_VERSION 1.2.0
 
-RUN apt update && apt install -y openssl curl ca-certificates wget \
-  && wget -O certstrap https://github.com/square/certstrap/releases/download/v${CERTSTRAP_VERSION}/certstrap-${CERTSTRAP_VERSION}-linux-amd64 \
-  && chmod +x certstrap \
-  && cp certstrap /usr/local/bin/
+RUN wget -O certstrap https://github.com/square/certstrap/releases/download/v${CERTSTRAP_VERSION}/certstrap-${CERTSTRAP_VERSION}-linux-amd64 \
+    && chmod +x certstrap \
+    && cp certstrap /usr/local/bin/

cf-acceptance-tests/Dockerfile

@@ -1,17 +1,17 @@
-FROM ubuntu:xenial
-
-RUN \
-  apt-get update && \
-  apt-get -y install \
-    build-essential \
-    wget \
-    curl \
-    openssh-client \
-    unzip \
-    python-pip \
-    jq \
-    git fossil mercurial bzr subversion \
-  && rm -rf /var/lib/apt/lists/*
+FROM ghcr.io/alphagov/paas/ubuntu:main
+
+RUN apt update \
+    && apt install -y \
+      build-essential \
+      openssh-client \
+      unzip \
+      python-pip \
+      jq \
+      git \
+      fossil \
+      mercurial \
+      bzr \
+      subversion
 
 ENV GOPATH /go
 ENV PATH /go/bin:/usr/local/go/bin:$PATH