rabbit_peer_discovery: Use alternative connection for the temporary hidden node

[Why]
We want to make sure that the queried remote node doesn't know about the
querying node. That's why we use a temporary hidden node in the first
place.

In fact, it is possible to start the temporary hidden node and
communicate with it using an alternative connection instead of the
regular Erlang distribution. This further ensures that the two RabbitMQ
nodes don't connect to each other while properties are queried.

[How]
We use the `standard_io` alternative connection. We need to use
`peer:call/4` instead of `erpc:call/4` to run code on the temporary
hidden node.

While here, we add assertions to verify that the three node didn't form
a full mesh network at the end of the query code.

Author: dumbbell

deps/rabbit/src/rabbit_peer_discovery.erl

@@ -392,15 +392,16 @@ query_node_props(Nodes) when Nodes =/= [] ->
     VMArgs3 = maybe_add_proto_dist_arguments(VMArgs2),
     VMArgs4 = maybe_add_inetrc_arguments(VMArgs3),
     VMArgs5 = maybe_add_tls_arguments(VMArgs4),
+    PeerStartArg0 = #{name => PeerName,
+                      args => VMArgs5,
+                      connection => standard_io,
+                      wait_boot => infinity},
     PeerStartArg = case Context of
                        #{nodename_type := longnames} ->
-                           #{name => PeerName,
-                             host => Suffix,
-                             longnames => true,
-                             args => VMArgs5};
+                           PeerStartArg0#{host => Suffix,
+                                          longnames => true};
                        _ ->
-                           #{name => PeerName,
-                             args => VMArgs5}
+                           PeerStartArg0
                    end,
     ?LOG_DEBUG("Peer discovery: peer node arguments: ~tp",
                [PeerStartArg]),
@@ -412,7 +413,7 @@ query_node_props(Nodes) when Nodes =/= [] ->
                [Peer],
                #{domain => ?RMQLOG_DOMAIN_PEER_DISC}),
             try
-                erpc:call(Peer, ?MODULE, do_query_node_props, [Nodes])
+                peer:call(Pid, ?MODULE, do_query_node_props, [Nodes], 180000)
             after
                 peer:stop(Pid)
             end;
@@ -658,6 +659,8 @@ query_node_props2([], NodesAndProps, ProxyGroupLeader) ->
     after 120_000 ->
               ok
     end,
+    ?assertEqual([], nodes()),
+    ?assert(length(NodesAndProps2) =< length(nodes(hidden))),
     NodesAndProps2.
 
 -spec get_node_start_time(Node, Unit, ProxyGroupLeader) -> StartTime when