'Get virtualization overhead required to build an instance of the
given flavor.
:param instance_info: Instance/flavor to calculate overhead for.
:returns: Overhead memory in MB.'

def estimate_instance_overhead(self, instance_info):

    memory_mb = instance_info['memory_mb']
    vcpus = instance_info.get('vcpus', 1)
    overhead = (((memory_mb * OVERHEAD_PER_MB) + (vcpus * OVERHEAD_PER_VCPU)) + OVERHEAD_BASE)
    overhead = math.ceil(overhead)
    return {'memory_mb': overhead}
