util: introduce concept of a system token into identities

util: introduce concept of a system token into identities

We want a way to distinguish between calls from a libvirt daemon, and a
regular client application when both are running as the same user
account. This is not possible with the current set of attributes
recorded against an identity, as there is nothing that is common to all
of the modular libvirt daemons, while distinct to all other processes.

We thus introduce the idea of a system token, which is simply a random
hex string that is only known by the libvirt daemons, to be recorded
against the system identity.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>