(#112,#113) fix service persist without keyward

```
rospy : rospy.ServiceProxy(name, service_class, persistent=True) roscpp :
createClient (const std::string &service_name, bool persistent=false, const
M_string &header_values=M_string())
```

I'm not sure if we should add keyward for persist or not in roseus case, but
this implementation support
```
ros::service-call (name value &optional (persist nil))
```