fix #1079

* move gossip/NCP off assuming anything about its address
  * use a single socket to send and receive gossip
  * remove --addr/-a from CLIs
  * rearrange networking utility code
  * use Arc<UdpSocket> to share the Sync-safe UdpSocket among threads
  * rename TestNode to Node

TODO:

  * re-enable 127.0.0.1 as a valid address in crdt
  * change repair request/response to a similar, single socket
  * pick cloned sockets or Arc<UdpSocket> for all these (rpu uses tryclone())
  * update contact_info with network truthiness instead of what the node
      says?

multinode-demo/wallet.sh

@@ -47,4 +47,4 @@ fi
 
 # shellcheck disable=SC2086 # $solana_wallet should not be quoted
 exec $solana_wallet \
-  -a 127.0.0.1 -l "$SOLANA_CONFIG_CLIENT_DIR"/leader.json -k "$client_id_path" --timeout 10 "$@"
+  -l "$SOLANA_CONFIG_CLIENT_DIR"/leader.json -k "$client_id_path" --timeout 10 "$@"