Return the VM's size. Used by create_node().

def get_size(vm_):
    '''
    Return the VM's size. Used by create_node().
    '''
    sizes = avail_sizes()
    vm_size = six.text_type(config.get_cloud_config_value(
        'size', vm_, __opts__, search_global=False
    ))

    if not vm_size:
        raise SaltCloudNotFound('No size specified for this VM.')

    if vm_size and six.text_type(vm_size) in sizes:
        return sizes[vm_size]['InstanceTypeId']

    raise SaltCloudNotFound(
        'The specified size, \'{0}\', could not be found.'.format(vm_size)
    )