fix autobahn client to process multi messages test case

turn out the autobahn server not only use single echo
message for all test case, but also use multi messages
response to measure performance.

examples/autobahn_client.nim

@@ -41,6 +41,7 @@ proc getCaseCount(): Future[int] {.async.} =
 
 proc generateReport() {.async.} =
   try:
+    trace "request autobahn server to generate report"
     let ws = await connectServer("/updateReports?agent=" & agent)
     while true:
       let buff = await ws.recv()
@@ -55,17 +56,24 @@ proc main() {.async.} =
   trace "case count", count=caseCount
 
   for i in 1..caseCount:
+    trace "runcase", no=i
     let path = "/runCase?case=$1&agent=$2" % [$i, agent]
     try:
       let ws = await connectServer(path)
+
+      while ws.readystate != ReadyState.Closed:
         # echo back
         let data = await ws.recv()
         let opCode = if ws.binary:
                        Opcode.Binary
                      else:
                        Opcode.Text
+
+        if ws.readyState == ReadyState.Closed:
+          break
+
         await ws.send(data, opCode)
-      await ws.close()
+
     except WebSocketError as exc:
       error "WebSocket error", exception = exc.msg