Restructured docker building

I have restructured the docker build process entirely, the binary gets
built outside of the docker build command, now we are managing all
dependencies with real Alpine packages and I have dropped features like
socat or the cron daemon.

Signed-off-by: Thomas Boerger <tboerger@suse.de>

docker/etc/s6/openssh/finish

@@ -0,0 +1,2 @@
+#!/bin/bash
+exit 0

docker/etc/s6/openssh/run

@@ -0,0 +1,6 @@
+#!/bin/bash
+[[ -f ./setup ]] && source ./setup
+
+pushd /root > /dev/null
+    exec gosu root /usr/sbin/sshd -E /var/log/sshd.log -D
+popd

docker/etc/s6/openssh/setup

@@ -0,0 +1,29 @@
+#!/bin/bash
+
+if [ ! -d /data/ssh ]; then
+    mkdir -p /data/ssh
+fi
+
+if [ ! -f /data/ssh/ssh_host_ed25519_key ]; then
+    echo "Generating /data/ssh/ssh_host_ed25519_key..."
+    ssh-keygen -t ed25519 -b 4096 -f /data/ssh/ssh_host_ed25519_key -N "" > /dev/null
+fi
+
+if [ ! -f /data/ssh/ssh_host_rsa_key ]; then
+    echo "Generating /data/ssh/ssh_host_rsa_key..."
+    ssh-keygen -t rsa -b 2048 -f /data/ssh/ssh_host_rsa_key -N "" > /dev/null
+fi
+
+if [ ! -f /data/ssh/ssh_host_dsa_key ]; then
+    echo "Generating /data/ssh/ssh_host_dsa_key..."
+    ssh-keygen -t dsa -f /data/ssh/ssh_host_dsa_key -N "" > /dev/null
+fi
+
+if [ ! -f /data/ssh/ssh_host_ecdsa_key ]; then
+    echo "Generating /data/ssh/ssh_host_ecdsa_key..."
+    ssh-keygen -t ecdsa -b 256 -f /data/ssh/ssh_host_ecdsa_key -N "" > /dev/null
+fi
+
+chown root:root /data/ssh/*
+chmod 0700 /data/ssh
+chmod 0600 /data/ssh/*