[ofw] CA attribute system_image_guid

[Sean Hefty]

>Pardon my ignorance....What in the world is a 'system_image_guid' and what
>would it be used for?

In extremely technical terms:

GUID associating this node with other nodes controlled
by common supervisory code. Provides a means for system
software to indicate the availability of multiple paths
to the same destination via multiple nodes. Set to zero if
indication of node association is not desired. The SystemImageGUID
may be the NodeGUID of one of the
associated nodes if that node is not field-replaceable

I.e. NodeGuid - guid of HCA
system image guid - guid of computer/system/host

- Sean