Use --server_name override when setting the host header

Summary: The `--server_name` override wasn't being honored when setting the host header, defaulting to the `--server` flag's value. This diff changes that.

Reviewed By: lnicco

Differential Revision: D50695638

fbshipit-source-id: f62d956a3f937ca3260a3e91862239eb2e700836

proxygen/httpclient/samples/httperf2/HTTPerf2.cpp

@@ -336,12 +336,17 @@ ClientRunner::ClientRunner(HTTPerfStats& parentStats,
     request_.setMethod(HTTPMethod::GET);
   }
 
+  serverName_ = FLAGS_server;
+  if (!FLAGS_server_name.empty()) {
+    serverName_ = FLAGS_server_name;
+  }
+
   if (FLAGS_http10) {
     request_.setHTTPVersion(1, 0);
   } else {
     request_.setHTTPVersion(1, 1);
     if (!FLAGS_nohost) {
-      request_.getHeaders().add(HTTP_HEADER_HOST, FLAGS_server);
+      request_.getHeaders().add(HTTP_HEADER_HOST, serverName_);
     }
   }
 
@@ -370,10 +375,6 @@ ClientRunner::ClientRunner(HTTPerfStats& parentStats,
       request_.getHeaders().add(headerName, header.substr(pos));
     }
   }
-  serverName_ = FLAGS_server;
-  if (!FLAGS_server_name.empty()) {
-    serverName_ = FLAGS_server_name;
-  }
 }
 
 void ClientRunner::run() {