fix(instrumentations): report statusCode passed to writeHead

Author: dszakallas

lib/instrumentations/core/http/server.js

@@ -120,7 +120,7 @@ function httpServer (listener, agent) {
           alreadyEnded = true
           writeHeadAlreadyCalled = true
           var ssTime = microtime.now()
-          var statusCode = response.statusCode || arguments[0]
+          var statusCode = arguments[0] || response.statusCode
           var tracerBriefcase = agent.storage.get('tracer.briefcase')
           if (!tracerBriefcase) {
             debug('#httpServer', '[Warning] lost tracer.briefcase context, falling back to SR briefcase')