We already have a read-only flag on InstanceState; maybe we should allow "identity" to be nil if read_only == true. That would let us use it here without caring about the agent ID.

c.f. https://github.com/rightscale/right_link/blob/efa14c2516b7f8344f38d6c65c2d2cfe6457ef64/lib/instance/instance_state.rb#L142