Indicate HTTP status code by library const (#703)

fission/migrate.go

@@ -101,7 +101,7 @@ func migrateDeleteTPR(c *cli.Context) error {
 	checkErr(err, "delete tpr resources")
 	defer resp.Body.Close()
 
-	if resp.StatusCode == 404 {
+	if resp.StatusCode == http.StatusNotFound {
 		msg := fmt.Sprintf("Server %v isn't support deleteTpr method. Use --server to point at a 0.4.0+ Fission server.", server)
 		fatal(msg)
 	}

fission/upgrade.go

@@ -249,7 +249,7 @@ func upgradeDumpState(c *cli.Context) error {
 	// check v1
 	resp, err := http.Get(u + "/environments")
 	checkErr(err, "reach fission server")
-	if resp.StatusCode == 404 {
+	if resp.StatusCode == http.StatusNotFound {
 		msg := fmt.Sprintf("Server %v isn't a v1 Fission server. Use --server to point at a pre-0.2.x Fission server.", u)
 		fatal(msg)
 	}