Add test for preempting a trajectory with SJTC

[fmauch]

Feature summary

Since we recently had the issue of the SJTC not correctly aborting motions if the trajectory action was aborted, we added a test that verifies that it now does. We could do the same for preempting a trajectory.

Related issues

• Fix sjtc to correctly aborts on violation of constraints  #810 contains the test and the fix for aborting due to constraint validations

Tasks

To complete this issue involves

• Make Unit test
• Test on real hardware