static ConnectionRegistry create(Configuration conf, User user) {
    Class<? extends ConnectionRegistry> clazz =
      conf.getClass(HConstants.CLIENT_CONNECTION_REGISTRY_IMPL_CONF_KEY,
        RpcConnectionRegistry.class, ConnectionRegistry.class);
    return ReflectionUtils.newInstance(clazz, conf, user);
  }
Returns the connection registry implementation to use.
<p/>
This is used when we do not have a connection url, we will use the old way to load the
connection registry, by checking the
{@literal HConstants#CLIENT_CONNECTION_REGISTRY_IMPL_CONF_KEY} configuration.
hbase-client/src/main/java/org/apache/hadoop/hbase/client/ConnectionRegistryFactory.java