Add OSSN-0012 - OpenSSL Heartbleed vulnerability

This adds OSSN-0012, which covers the OpenSSL Heartbleed
vulnerability.  This isn't a vulnerability in OpenStack itself, but
OpenStack deployments are likely affected since they would be using
OpenSSL for SSL/TLS.

Change-Id: I2db43e23dc0b090887e937be6188b64e2a0a2ad5