Make the node call listenHTTP first

The runTask() call will spawn a new fiber and
and switch to the new fiber immediately.
However we want to start listening for incoming
requests before doing network discovery.

Using setTimer with a zero timeout (a.k.a. schedule())
makes the node open a listening port right away,
rather than waiting for the first discovery round
to complete.

It increases the node's connectivity to other nodes
which may want to establish a connection,
and consequently reduces CI failures.

Part of: #1117

source/agora/node/Runner.d

@@ -22,13 +22,16 @@ import agora.utils.Log;
 
 import ocean.util.log.ILogger;
 
+import vibe.core.core;
 import vibe.http.server;
 import vibe.http.router;
 import vibe.web.rest;
 
 import std.file;
 import std.format;
 
+import core.time;
+
 mixin AddLogger!();
 
 /*******************************************************************************
@@ -86,7 +89,7 @@ public FullNode runNode (Config config)
             res.writeVoidBody();
         });
 
-    node.start();  // asynchronous
+    setTimer(0.seconds, &node.start, false);  // asynchronous
 
     log.info("About to listen to HTTP: {}", settings.port);
     listenHTTP(settings, router);