Add a default handler for the / route

Before this change, if the user doesn't define a route for /, the
router happily 404s at that path.  This breaks GKE Ingress, which uses
that request as a health check.  So this change adds a handler for
"GET /", unless the user already has one.

Also, log the delay for slow requests.

router/functionHandler.go

@@ -86,11 +86,12 @@ func (fh *functionHandler) tapService(serviceUrl *url.URL) {
 	}
 	err := fh.poolmgr.TapService(serviceUrl)
 	if err != nil {
-		log.Printf("tap service error: %v", serviceUrl.String())
+		log.Printf("tap service error for %v: %v", serviceUrl.String(), err)
 	}
 }
 
 func (fh *functionHandler) handler(responseWriter http.ResponseWriter, request *http.Request) {
+	reqStartTime := time.Now()
 
 	// cache lookup
 	serviceUrl, err := fh.fmap.lookup(&fh.Function)
@@ -150,5 +151,9 @@ func (fh *functionHandler) handler(responseWriter http.ResponseWriter, request *
 			initalTimeout: 50 * time.Millisecond,
 		},
 	}
+	delay := time.Now().Sub(reqStartTime)
+	if delay > 100*time.Millisecond {
+		log.Printf("Request delay for %v: %v", serviceUrl, delay)
+	}
 	proxy.ServeHTTP(responseWriter, request)
 }