In this case, qmemman would not manage to get any memory state for such
VM, so memory_current would be 'None'. But later it would perform
arithmetics on it, which would result in qmemman crash (TypeError
exception).
FixesQubesOS/qubes-issues#1601
When VM got some memory assigned, balloon driver may not pick it up
immediatelly and the memory will still be seen as "free" by Xen, but VM
can use (request) it at any time. Qmemman needs to take care of such
memory (exclude it from "free" pool), otherwise it would redistribute it
to other domains, allowing the original domain to drain Xen memory pool.
Do this by redefining DomainState.memory_actual - it is now amount of
memory available to the VM (currently used, or possibly used). Then
calculate free memory by subtracting memory allocated but not used
(memory_target-memory_current).
FixesQubesOS/qubes-issues#1389
