Don't spam the portfile during TestServer startup

Prior to this change, the server test was repeatedly performing io on
the portfile while the server was starting up. This adds a modest sleep
so that the test is just as responsive without doing needless io.

server-test/src/test/scala/testpkg/TestServer.scala

@@ -187,6 +187,7 @@ case class TestServer(
         hostLog("waiting for the server...")
         nextLog = 10.seconds.fromNow
       }
+      Thread.sleep(10) // Don't spam the portfile
     }
     if (deadline.isOverdue) sys.error(s"Timeout. $portfile is not found.")
     if (!process.isAlive) sys.error(s"Server unexpectedly terminated.")