Fix deadlock in standalone mcrouter on invalid config (#455)

Summary:
After 6c2142a, standalone mcrouter now deadlocks if the router configuration was incorrect. Spotted on #449, where `test_unknown_named_handles` started failing due to the mcrouter process being tested never exiting.

GDB [indicates](https://gist.github.com/mszabo-wikia/47916c5655deffdb95332e972a52caf8) a deadlock between three threads:
```
(gdb) info threads
  Id   Target Id                                          Frame
* 1    Thread 0x7f7b4cce1e00 (LWP 211878) "mcrouter"      syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  2    Thread 0x7f7b43fff6c0 (LWP 211882) "mcr-cpuaux-0"  syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
  3    Thread 0x7f7b49e0a6c0 (LWP 211879) "IOThreadPool0" syscall () at ../sysdeps/unix/sysv/linux/x86_64/syscall.S:38
```

* Thread 1, the main thread, has triggered exit() and is waiting on the auxiliary thread pool to be destroyed.
* Thread 2, an auxiliary thread pool thread, is in the process of destroying the CarbonRouterInstance due to
6c2142a and is blocked on destroying the virtual EVBs by child proxies. These however are ultimately sourced from the IO thread pool which is also used by AsyncMcServer.
* Thread 3, an IO thread pool thread, is blocked by AsyncMcServer which is waiting to be started by later initialization code that never runs due to the config error, preventing the IO thread pool itself from being destroyed.

Fix it by initializing the AsyncMcServer only after the router has been initialized.

Pull Request resolved: #455

Reviewed By: lenar-f

Differential Revision: D67069250

Pulled By: disylh

fbshipit-source-id: d6edff40b9f40ee7925e94c4ee9cf985c10a98de

mcrouter/Server-inl.h

@@ -310,11 +310,6 @@ bool runServerDual(
     auto evbs = extractEvbs(*ioThreadPool);
     CHECK_EQ(evbs.size(), mcrouterOpts.num_proxies);
 
-    // Create AsyncMcServer instance
-    asyncMcServer =
-        std::make_shared<AsyncMcServer>(detail::createAsyncMcServerOptions(
-            mcrouterOpts, standaloneOpts, &evbs));
-
     // Create CarbonRouterInstance
     if (standaloneOpts.remote_thread) {
       router =
@@ -328,6 +323,11 @@ bool runServerDual(
       return false;
     }
 
+    // Create AsyncMcServer instance
+    asyncMcServer =
+        std::make_shared<AsyncMcServer>(detail::createAsyncMcServerOptions(
+            mcrouterOpts, standaloneOpts, &evbs));
+
     setupRouter<RouterInfo>(mcrouterOpts, standaloneOpts, router, preRunCb);
 
     // Create CarbonRouterClients for each worker thread
@@ -515,10 +515,6 @@ bool runServer(
     // Get EVB of main thread
     auto localEvb = ioThreadPool->getEventBaseManager()->getEventBase();
 
-    asyncMcServer =
-        std::make_shared<AsyncMcServer>(detail::createAsyncMcServerOptions(
-            mcrouterOpts, standaloneOpts, &evbs));
-
     if (standaloneOpts.remote_thread) {
       router =
           CarbonRouterInstance<RouterInfo>::init("standalone", mcrouterOpts);
@@ -531,6 +527,10 @@ bool runServer(
       return false;
     }
 
+    asyncMcServer =
+        std::make_shared<AsyncMcServer>(detail::createAsyncMcServerOptions(
+            mcrouterOpts, standaloneOpts, &evbs));
+
     setupRouter<RouterInfo>(mcrouterOpts, standaloneOpts, router, preRunCb);
 
     auto shutdownStarted = std::make_shared<std::atomic<bool>>(false);