Dockerfile: Streamline tarball extraction
Dockerfile: Streamline tarball extraction

* No point in writing it to the disk and then deleting it
* Extract it in place

hjnijlunsing/docker-openvpn-armhf,elie195/docker-openvpn,morcavon/docker-openvpn,myplacedk/docker-openvpn,mouyigang/docker-openvpn,richnologies/docker-openvpn,shanonvl/docker-openvpn,gl-sergei/docker-openvpn,kylemanna/docker-openvpn,csakoda/docker-openvpn,slamont/docker-openvpn,caervs/docker-openvpn,dx9/docker-openvpn,rdev02/docker-openvpn