fix json error after downgrade

[bullet1337]

Error after downgrading from 21.11 to 21.8

ClickHouse 21.11 creates a file with "clickhouse" element, while 21.8 expects "yandex"

<Error> Application: Caught exception while loading metadata: Poco::Exception. Code: 1000, e.code() = 0, e.displayText() = JSONException: JSON: there is no element 'yandex' in object., Stack trace (when copying this message, always include the lines below)

[CLAassistant]

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