Calling /start during an active transition callback should automatically fail

[asiron]

If any transition callback is being executed, then calling another state transition service should fail.

For example, if onConfigure or onManagedConfigure is being executed, then calling my_node/start should fail, as the node is not ready to be started, it should also return an appropriate error together with the failure message.

This should only be possible at the beginning of the robot_activity operation (init call) as transitions can only be invoked by ROS service, which are all grouped on a separate callback queue and a separate thread.