multi-stage dockerbuild, so openvpn needs to be added later

Dockerfile

@@ -9,9 +9,14 @@ WORKDIR $GOPATH
 RUN go get -u github.com/OperatorFoundation/shapeshifter-dispatcher/shapeshifter-dispatcher
 RUN strip $GOPATH/bin/shapeshifter-dispatcher
 
-RUN update-alternatives --set iptables /usr/sbin/iptables-legacy
-
 FROM registry.git.autistici.org/ai3/docker/chaperone-base
+RUN apt-get -q update && env DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
+    openvpn netcat-openbsd iptables\
+&& rm -rf /var/lib/apt/lists/*
+
+# needed for buster, but chaperone-base image is still stretch
+#RUN update-alternatives --set iptables /usr/sbin/iptables-legacy
+
 COPY --from=build /go/bin/shapeshifter-dispatcher /usr/local/bin/shapeshifter-dispatcher
 COPY chaperone.d/ /etc/chaperone.d