**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.

{
    shared->server_ports.emplace(std::move(port_name), port);
}
UInt16 Context::getServerPort(const String & port_name) const
{
    auto it = shared->server_ports.find(port_name);
    if (it == shared->server_ports.end())
        throw Exception(ErrorCodes::BAD_GET, "There is no port named {}", port_name);
    else
        return it->second;
}
std::shared_ptr<Cluster> Context::getCluster(const std::string & cluster_name) const
{
    auto res = getClusters()->getCluster(cluster_name);
    if (res)
        return res;
    if (!cluster_name.empty())
        res = tryGetReplicatedDatabaseCluster(cluster_name);
    if (res)
        return res;
    throw Exception("Requested cluster '" + cluster_name + "' not found", ErrorCodes::BAD_GET);
}
std::shared_ptr<Cluster> Context::tryGetCluster(const std::string & cluster_name) const