Add tests for velocity_controllers::JointTrajectoryController

[miguelprada]

This PR adds a VelocityJointInterface to RRBot, and duplicates the tests being run for the position-based joint trajectory controller.

[bmagyar]

ok Miguel, one last thing: could you please squash your commits on this PR?

[miguelprada]

Done. I also rebased on top of the current kinetic-devel while I was on it, since the only commit that was there was something on the travis configuration. Hope this is fine.

[miguelprada]

After squashing and rebasing I found a compilation error which made the CI job fail. It had to do with the API change introduced in ros-controls/ros_control@afaf940, and I'm not quite sure how it flew under my radar (probably some messed up workspace with indigo-devel branch of ros_control).

Anyways, after fixing it, the travis job still fails, only this time on some diff_drive_controller test. Don't think there's anything I should do about this, right?

[bmagyar]

Thanks for sticking around with this one, merging...