- Previously it was hard to check which state the gripper was in
(GRAB/GRABBED/ etc), not even whether it was correctly initialized, this
commit adds that functionality
- When the gripper was uninitialized, the error message popped up
everytime the module had 'any' vehicle command received. But we should
be spamming only when we do actually get 'DO_GRIPPER' command received,
this commit adds that feature
- Also converted error messages for CLI when gripper test functinality
fails, so that user would get a feedback (originally, the PX4_DEBUG was
of course not outputting everything)