ports: add openvpn-2.3.4

The port is succesfully tested with echo test, lighttpd and
rdesktop. DHCP over OpenVPN is not tested, therefore the ip address etc.
needs to be specified manually.
openssl: use Genode specific RAND backend

For now, we merely provide "/dev/random".
openssl: update to version 1.0.1i
libports: add jitterentropy-20140411