This is a small cleanup of find_openssl_binary(). It tries also
to find a newer openssl version which we could need for any
new features. As stated in the comment at some point we should
decide whether we stick with our old version or rather supply
a new one. (xmpp-server is also not builtin for our 1.0.2) or
maybe find a good way (code) how to use both.
Also it looks for socat and if found it populates the according
global var.
It does a minor resort of global vars in the beginning.
.. see also #1559.
It "mkdirs" the needed etc and bin directories first, then copies
stuff over. It also reduces a few layers.
Also it corrects a mistake in the Readme.md (docker exec --> run)
Thanks for the discussion @Alex131089
