Fix deadlock in standalone mcrouter on invalid config

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

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.

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);