[cob_drive_wheel] fix physics for gazebo - base drifting

[fmessmer]

as mentioned and observed by @ipa-pfs both cob and raw are spinning when simulated in gazebo although no command is sent, i.e .they start spinning right after being spawned

this seems to be a physics (inertia, friction) problem of the base, most likely the drive_wheel model, as it can be observed that:

• no command is sent by cob_omni_drive_controller
• wheels are not oriented towards the observed motion
• not all wheels are rotating/moving (check frames in rviz and gazebo in wireframe view)

[fmessmer]

this https://github.com/ipa320/cob_control/issues/187#issuecomment-462286083 seems to be related
@bvanelli FYI

[fmessmer]

see ipa320/cob_simulation#165
@bvanelli @ipa-pfs FYI

[fmessmer]

I think the problem was a missing query for physics_type in the initSim function, which is used in https://github.com/ros-simulation/gazebo_ros_pkgs/blob/kinetic-devel/gazebo_ros_control/src/default_robot_hw_sim.cpp#L359-L372

this is fixed in ipa320/cob_gazebo_plugins@72fbd71

please re-open in case you are still facing this problem