Nested policy configuration

[glebkin]

Get nested policy configuration back:

example.org {
    fanout . 127.0.0.1:9005 127.0.0.1:9006 127.0.0.1:9007 {
      policy weighted-random {
        server-count 2
        load-factor 50 70 100
      }
    }
}

Instead of:

example.org {
    fanout . 127.0.0.1:9005 127.0.0.1:9006 127.0.0.1:9007 {
      policy weighted-random
      weighted-random-server-count 2
      weighted-random-load-factor 50 70 100
    }
}