Integrate firewall on linux client
For the fail close, Elijah has written a nice firewall script that blocks outgoing traffic except for the tunnel gateway(s). We need to be able to quickly integrate the firewall with openvpn. The goal is to be able to fail close on linux, to begin with, for the 0.5.1 release.
(from redmine: created on 2014-04-29, closed on 2014-05-19, relates #3972 (closed), relates #3860 (closed), relates #5622 (closed), relates #5669 (closed), relates #5691 (closed), relates #5692 (closed), precedes #5615 (closed), precedes #5616 (closed), precedes #5617 (closed), precedes #5618 (closed), precedes #5619 (closed), precedes #5620 (closed), precedes #5627 (closed), precedes #5630 (closed), precedes #5631 (closed), precedes #5650 (closed), precedes #5651 (closed), precedes #5655 (closed), precedes #5663 (closed), precedes #5693 (closed))