**Describe the bug**
The ClickHouse client freezes when executing `ALTER TABLE` with `ADD COLUMN` and `MODIFY ORDER` on a table built using Replicated Versioned Collapsing Merge Tree engine.

**How to reproduce**
* ClickHouse client version 20.10.1.1.
Connecting to localhost:9000 as user default.
Connected to ClickHouse server version 20.10.1 revision 54440.

* `CREATE TABLE` statements
```
SHOW CREATE TABLE table0

┌─statement──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┐
│ CREATE TABLE default.table0
(
    `d` Date,
    `a` String,
    `b` UInt8,
    `x` String,
    `y` Int8,
    `version` UInt64,
    `sign` Int8 DEFAULT 1
)
ENGINE = ReplicatedVersionedCollapsingMergeTree('/clickhouse/tables/{shard}/table0', '{replica}', sign, version)
PARTITION BY y
ORDER BY d
SETTINGS index_granularity = 8192 │
└────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┘

1 rows in set. Elapsed: 0.004 sec.
```

* Queries to run that lead to unexpected result
```
ALTER TABLE table0 ADD COLUMN order UInt32, MODIFY ORDER BY (d, order)
```
remove_futures.emplace_back(zookeeper->tryAsyncMulti(ops));
                }
            }
            for (auto & future : remove_futures)
            {
                auto response = future.get();
                if (response.error == Coordination::Error::ZOK || response.error == Coordination::Error::ZNONODE)
                    continue;
                if (Coordination::isHardwareError(response.error))
                {
                    success = false;
                    continue;
                }
                throw Coordination::Exception(response.error);
            }
        }
        catch (Coordination::Exception & e)
        {
            success = false;
            if (Coordination::isHardwareError(e.code))
                tryLogCurrentException(log, __PRETTY_FUNCTION__);
            else
                throw;
        }
        if (!success && num_tries < max_retries)
            std::this_thread::sleep_for(std::chrono::milliseconds(1000));
    }
    return success;
}
void StorageReplicatedMergeTree::removePartsFromZooKeeper(