Fix move to initial state service

[cmower]

The service is initialized here:

https://github.com/cmower/ros_pybullet_interface/blob/2680c302114ac84f40b8946aa77ff1e7e9f81f84/ros_pybullet_interface/src/rpbi/pybullet_robot.py#L37

This uses the ResetJointState service template. However, the joint_state in the service request is ignored (the initial joint state is retrieved from the configuration file).

When calling the service it requires the user to pass an empty JointState message, as follows

duration = 5.0  # secs
resp = srv_handler(JointState(), duration)

Ideally this should be

duration = 5.0  # secs
resp = srv_handler(duration)