machine pool controller for automatic provisioning

[Unix4ever]

The controller should take MachineClassStatus and AutoscalingGroup as the inputs. MachineClassStatus will provide machine pressure information, AutoscalingGroup will keep the configuration of the scaling: the number of machines to keep running unallocated, the timeout for the unused machine request removal and the configuration for the machine requests.

It should also take MachineStatusLabels resource as the input to keep track of which machine requests are in use and which are not.

The output of this controller will be a MachinePool resource.

MachineStatus resources added by the cloud provider should be labeled with the MachinePool label. Then the machine class should select the machines which are labeled with this machine pool label.