@InterfaceAudience.LimitedPrivate(HBaseInterfaceAudience.HBCK)
  default Hbck getHbck(ServerName masterServer) throws IOException {
    return toAsyncConnection().getHbck(masterServer);
  }
Retrieve an Hbck implementation to fix an HBase cluster. The returned Hbck is not guaranteed to
be thread-safe. A new instance should be created by each thread. This is a lightweight
operation. Pooling or caching of the returned Hbck instance is not recommended. <br>
The caller is responsible for calling {@link Hbck#close()} on the returned Hbck instance. <br>
This will be used mostly by hbck tool. This may only be used to by pass getting registered
master from ZK. In situations where ZK is not available or active master is not registered with
ZK and user can get master address by other means, master can be explicitly specified.
@param masterServer explicit {@link ServerName} for master server
@return an Hbck instance for a specified master server
hbase-client/src/main/java/org/apache/hadoop/hbase/client/Connection.java