Add OSSN-0028 - Nova leaks hypervisor host SMBIOS serial number to guests

This add a new OSSN about the SMBIOS serial number of the underlying
compute node hardware being leaked to guest instances.

Closes-bug: #1337349
Change-Id: I724c4117b6ecf28db06b9d601e29e789ac6d2bff
Merge "Add OSSN-0028 - Nova leaks hypervisor host SMBIOS serial number to guests"