DSA-3900-1 openvpn -- security update

Several issues were discovered in openvpn, a virtual private network application:

https://www.debian.org/security/2017/dsa-3900

pi@noads:~ $ apt-cache policy openvpn
openvpn:
  Installed: 2.3.4-5+deb8u2
  Candidate: 2.3.4-5+deb8u2