'Get the number of volumes in a storage group.
:param array: the array serial number
:param storage_group_name: the storage group name
:returns: num_vols -- int'

def get_num_vols_in_sg(self, array, storage_group_name):

    num_vols = 0
    storagegroup = self.get_storage_group(array, storage_group_name)
    try:
        num_vols = int(storagegroup['num_of_vols'])
    except (KeyError, TypeError):
        pass
    return num_vols
