handle error when getting hostname in info api

Signed-off-by: allencloud <allen.sun@daocloud.io>

daemon/info.go

@@ -133,9 +133,13 @@ func (daemon *Daemon) SystemInfo() (*types.Info, error) {
 		v.CPUSet = sysInfo.Cpuset
 	}
 
-	if hostname, err := os.Hostname(); err == nil {
-		v.Name = hostname
+	hostname := ""
+	if hn, err := os.Hostname(); err != nil {
+		logrus.Warnf("Could not get hostname: %v", err)
+	} else {
+		hostname = hn
 	}
+	v.Name = hostname
 
 	return v, nil
 }