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/nsswitch.conf

@@ -0,0 +1,15 @@
+# /etc/nsswitch.conf
+
+passwd:         compat
+group:          compat
+shadow:         compat
+
+hosts:          files dns
+networks:       files
+
+protocols:      db files
+services:       db files
+ethers:         db files
+rpc:            db files
+
+netgroup:       nis