Make test_epmd more robust by performing an actual query on epmd

test_epmd ensured that epmd is running on CI by trying to connect to it.
However, in some cases, this connection test succeeded while epmd would
not be ready yet and would close the socket when trying to register.
See for example this run: https://github.com/pguyot/AtomVM/actions/runs/19780234793/job/56679370750

Replace test with querying for registered nodes to ensure epmd is indeed
ready.

Signed-off-by: Paul Guyot <pguyot@kallisys.net>

Author: pguyot

tests/libs/estdlib/test_epmd.erl

@@ -97,19 +97,14 @@ ensure_epmd("ATOM") ->
 
 ensure_epmd_connect_loop(0) ->
     io:format("Coult not connect to epmd\n"),
-    exit(timeout);
+    {error, timeout};
 ensure_epmd_connect_loop(N) ->
-    {ok, Socket} = socket:open(inet, stream, tcp),
-    Result = socket:connect(Socket, #{addr => {127, 0, 0, 1}, port => ?EPMD_PORT, family => inet}),
-    socket:close(Socket),
-    case Result of
-        ok ->
+    case erl_epmd:names("127.0.0.1") of
+        {ok, _} ->
             ok;
-        {error, econnrefused} ->
-            timer:sleep(100),
-            ensure_epmd_connect_loop(N - 1);
-        {error, closed} ->
-            timer:sleep(100),
+        {error, Reason} ->
+            io:format("Could not connect to epmd -- error = ~p, retrying (N = ~p)\n", [Reason, N]),
+            timer:sleep(500),
             ensure_epmd_connect_loop(N - 1)
     end.
 
@@ -153,14 +148,24 @@ start_epmd() ->
     Platform = erlang:system_info(machine),
     case has_epmd(Platform) of
         true ->
-            ok = ensure_epmd(Platform),
-            % on CI, epmd may be slow to accept connections
-            ensure_epmd_connect_loop(50),
-            ok;
+            start_epmd(Platform, 5);
         false ->
             {error, not_found}
     end.
 
+start_epmd(_Platform, 0) ->
+    exit(timeout);
+start_epmd(Platform, N) ->
+    ok = ensure_epmd(Platform),
+    % on CI, epmd may be slow to accept connections
+    case ensure_epmd_connect_loop(5) of
+        ok ->
+            ok;
+        {error, timeout} ->
+            stop_epmd(Platform),
+            start_epmd(Platform, N - 1)
+    end.
+
 stop_epmd() ->
     Platform = erlang:system_info(machine),
     case has_epmd(Platform) of