change hw_state_ to hw_position for only position command rrbot.

[benthebear93]

As a beginner, i been reading code for rrbot and diffbot together.

One thing that made me little confusing was variable's name.

variable for state of position only rrbot is

std::vector<double> hw_states_;

variable for diffbot is

  std::vector<double> hw_positions_;
  std::vector<double> hw_velocities_;

and rrbot_system_multi_interface has

  std::vector<double> hw_states_positions_;
  std::vector<double> hw_states_velocities_;
  std::vector<double> hw_states_accelerations_;

it's trivial but wouldn't it be better to unify the names of variables?

[bmagyar]

Such suggestions are best communicated through PRs ;)

[benthebear93]

@bmagyar I will think about more general names to unify the variables names for command and state interface and do the PR.