expected conditions is a dict and each value is an object of ExpectedCondition instead of a list

When parsing expected conditions, all items are placed into a dict with attribute as key and condition as value. Each value in the expected condition map is an object of ExpectedCondition instead of a list. The following code in cassandra_impl.py assumes it is a list.

    def _append_expected_conditions(self, expected_condition_map, schema,
                                    query_builder):
        init_length = len(query_builder)

        for attr_name, cond_list in expected_condition_map.iteritems():
            for condition in cond_list:
                self._append_expected_condition(
                    attr_name, condition, query_builder,
                    attr_name in schema.attribute_type_map
                )
                query_builder.append(" AND ")

        if len(query_builder) > init_length:
            query_builder.pop()

It should be changed to:

    def _append_expected_conditions(self, expected_condition_map, schema,
                                    query_builder):
        init_length = len(query_builder)

        for attr_name, condition in expected_condition_map.iteritems():
            self._append_expected_condition(
                attr_name, condition, query_builder,
                attr_name in schema.attribute_type_map
            )
            query_builder.append(" AND ")

        if len(query_builder) > init_length:
            query_builder.pop()

I have tried the fix with delta_item and update_item with conditions and the fix works. Without the fix, the conditional update and delete would fail.