Estimate time left for booting machines

[dynamiccast]

When a machine is booting, if the driver can estimate the time left for a machine to boot, it should be able to return the information on a call to GET /api/machine/{:id}.

While this will remain a large evaluation, this could help the user to know how much time he will have to wait for his machines to be available.

This implies to add a new field bootPercentage in machine's model.If set to null one should considered booting time evaluation is deactivated.