Allow to provide default CPU/memory values on workers

[edigaryev]

One of the customers reached to us and asked for this feature.

The use-case is that each worker can have different specs, and the user wants to maximize the amount of resources used in the presence of 2 VMs per host limitation imposed by Apple.

We could probably extend the v1.Worker structure and add an option to orchard worker run that will update two new fields in that structure: CPUDefault and MemoryDefault. These values will be per-VM.

Afterwards, when the VM is scheduled, its actual CPU and memory values will be updated in case none were explicitly specified at the moment of creation.

In v1.VM we probably need to add something like CPUActual and MemoryActual to avoid overwriting the original values so that when the VM is re-scheduled, we'd be able to know whether the original values indicated by the user were unset.