Update SSL/TLS reccomendations in security guide

[Bryan D. Payne]

In the post-POODLE world we should probably update the SSL/TLS recommendations in the security guide. This is a reminder to do that.

Recommendations should be TLS v1 at a minimum for services that require broad client compatibility and TLS v1.2 only for services where you control the client and server sides.

Cipher suites should probably be revised as well. When using TLS v1.2 it should probably be limited to only ECDHE-ECDSA-AES256-GCM-SHA384 and when using TLS v1+ it should probably be HIGH:!aNULL:!eNULL:!DES:!3DES. Deployers should make sure to always include dhparams as well.

Let's also double check my recommendations above :-)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/135844

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/135844
Committed: https://git.openstack.org/cgit/openstack/security-doc/commit/?id=a9096790944a2cf3a4cd8eb415802e91fda3edb9
Submitter: Jenkins
Branch: master

commit a9096790944a2cf3a4cd8eb415802e91fda3edb9
Author: Tom Fifield <email address hidden>
Date: Thu Nov 20 12:46:59 2014 +0800

    Fix recommendations post-POODLE

    The POODLE attack compromised the security of SSLv3, and as
    Bryan Payne notes in the bug report, we should no longer be
    recommending its use.

    This patch implements the suggestions from the bug report to
    fix this, and add additional information on cipher suites.

    Change-Id: Ife4ba2fb95682b064e913730a956cb0f77bb9c1e
    Closes-Bug: 1389706