Hard-coded joints for the UR5

[AndyZe]

This is a hack in teach_motions.py that will prevent the code from workign on other types of robot. It was necessary because Clearpath's simulation has an extra joint in the MoveGroup vs. Vaultbot:

This is a hack for the UR5 simulation

if len(self.joint_names[arm_index]) == 7:
self.joint_names[arm_index] = self.joint_names[arm_index][:-1]

(Trims off any joints beyond the first 6)