SECURITY: New document describing proposed security process for OVS.

SECURITY: New document describing proposed security process for OVS.

Open vSwitch needs some kind of process for handling vulnerabilities.  So
far, we've been pretty lucky that way, but it can't last forever, and I
think we'll be better off if we have at least the outline of an established
process whenever a significant vulnerability comes along.  Here's my draft
of a process based on the documentation of the OpenStack process at
https://wiki.openstack.org/wiki/Vulnerability_Management.

I don't have a lot of experience with this kind of thing myself, so I'd
appreciate critical review from anyone who does.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Reviewed-by: Flavio Leitner <fbl@redhat.com>
Acked-by: Justin Pettit <jpettit@nicira.com>
Acked-by: Thomas Graf <tgraf@noironetworks.com>