Unify return_type nomenclature in hardware_interface and controller_interface

[v-lopez]

I propose the name change to keep the same nomenclature as for hardware_interfaces. What do you think?

  return controller_interface::return_type::OK;

Originally posted by @destogl in #139 (comment)

hardware_interface uses OK and controller_interface uses SUCCESS

[bmagyar]

I agree and I think we should pick the shorter one, I vote for OK.

[destogl]

I vote also foe OK. It is a bit broader term, but still with a clear meaning.

[Karsten1987]

OK sounds good to me, too.

[v-lopez]

All right, I'll do after #139 is merged to avoid conflicts

[destogl]

So we go with OK. Rename return_type::SUCCESS everywhere to return_type:OK. But keep SUCCESS where it is defined and make its value equal to OK. Mark SUCCESS is deprecated.