**Describe the issue**
ClickHouse is unable to start up after upgrading from 20.8 to 21.8. 

There is a replicated table with `:` in zk path and it couldn't be loaded with:

`2021.09.15 03:49:58.435071 [ 633075 ] {} <Error> Application: DB::Exception: Unknown auxiliary ZooKeeper name '/test_prefix'. If it's required it can be added to the section <auxiliary_zookeepers> in config.xml: Cannot attach table `db1`.`table1` from metadata file /var/lib/clickhouse/metadata/db1/table1.sql from query ATTACH TABLE db1.table1 (`field1` String, `date` Date) ENGINE = ReplicatedMergeTree('/test_prefix:db1/{shard}/table1', '{replica}') PARTITION BY toMonth(date) PRIMARY KEY field1 ORDER BY field1 SETTINGS index_granularity = 8192: while loading database `db1` from path /var/lib/clickhouse/metadata/db1
`

**Expected behavior**
ClickHouse server is able to startup after upgrade without schema change. "test_prefix" in "/test_prefix:db1/{shard}/table1" is not interpreted as an auxiliary ZooKeeper name.

getSettingsRef().background_fetches_pool_size,
        getSettingsRef().background_fetches_pool_size,
        CurrentMetrics::BackgroundFetchesPoolTask
    );
    LOG_INFO(shared->log, "Initialized background executor for fetches with num_threads={}, num_tasks={}",
        getSettingsRef().background_fetches_pool_size, getSettingsRef().background_fetches_pool_size);
    shared->common_executor = OrdinaryBackgroundExecutor::create
    (
        "Common",
        getSettingsRef().background_common_pool_size,
        getSettingsRef().background_common_pool_size,
        CurrentMetrics::BackgroundCommonPoolTask
    );
    LOG_INFO(shared->log, "Initialized background executor for common operations (e.g. clearing old parts) with num_threads={}, num_tasks={}",
        getSettingsRef().background_common_pool_size, getSettingsRef().background_common_pool_size);
    shared->is_background_executors_initialized = true;
}
MergeMutateBackgroundExecutorPtr Context::getMergeMutateExecutor() const
{
    return shared->merge_mutate_executor;
}
OrdinaryBackgroundExecutorPtr Context::getMovesExecutor() const
{
    return shared->moves_executor;
}
OrdinaryBackgroundExecutorPtr Context::getFetchesExecutor() const
{
    return shared->fetch_executor;
}
OrdinaryBackgroundExecutorPtr Context::getCommonExecutor() const