Fix beast::asio failures on OS X.

There are 38 unittest failures on OS X.  These changes address all of
them by adjusting which side of the socket (send or receive) gets
shut down.  In each case, the failure was 'Socket is not connected'.
I've interpreted that to mean that the other thread had already shut
down its side of the connection.

src/beast/modules/beast_asio/tests/TestPeerLogicAsyncClient.cpp

@@ -108,7 +108,7 @@ void TestPeerLogicAsyncClient::on_read_final (error_code const& ec, std::size_t)
         {
             // on_shutdown will call finished ()
             error_code ec;
-            on_shutdown (socket ().shutdown (Socket::shutdown_both, ec));
+            on_shutdown (socket ().shutdown (Socket::shutdown_send, ec));
         }
     }
     else
@@ -137,7 +137,7 @@ void TestPeerLogicAsyncClient::on_shutdown (error_code const& ec)
         {
             if (socket ().needs_handshake ())
             {
-                socket ().shutdown (Socket::shutdown_both, error ());
+                socket ().shutdown (Socket::shutdown_send, error ());
             }
 
             if (! error ())

src/beast/modules/beast_asio/tests/TestPeerLogicAsyncServer.cpp

@@ -90,7 +90,7 @@ void TestPeerLogicAsyncServer::on_write (error_code const& ec, std::size_t bytes
         // on_shutdown will call finished ()
         // we need another instance of ec so we can call on_shutdown()
         error_code ec;
-        on_shutdown (socket ().shutdown (Socket::shutdown_both, ec));
+        on_shutdown (socket ().shutdown (Socket::shutdown_receive, ec));
     }
 }
 
@@ -102,7 +102,7 @@ void TestPeerLogicAsyncServer::on_shutdown (error_code const& ec)
         {
             if (socket ().needs_handshake ())
             {
-                socket ().shutdown (Socket::shutdown_both, error ());
+                socket ().shutdown (Socket::shutdown_receive, error ());
             }
 
             if (success (socket ().close (error ())))

src/beast/modules/beast_asio/tests/TestPeerLogicSyncClient.cpp

@@ -94,9 +94,10 @@ void TestPeerLogicSyncClient::on_connect ()
     {
         if (failure (socket ().shutdown (error ()), true))
             return;
+        error () = error_code ();
     }
 
-    if (failure (socket ().shutdown (Socket::shutdown_both, error ())))
+    if (failure (socket ().shutdown (Socket::shutdown_send, error ())))
         return;
 
     if (failure (socket ().close (error ())))

src/beast/modules/beast_asio/tests/TestPeerLogicSyncServer.cpp

@@ -72,7 +72,7 @@ void TestPeerLogicSyncServer::on_connect ()
             return;
     }
 
-    if (failure (socket ().shutdown (Socket::shutdown_both, error ())))
+    if (failure (socket ().shutdown (Socket::shutdown_send, error ())))
         return;
 
     if (failure (socket ().close (error ())))