[BUG] Robot::busy() gives false negative

[isa-9]

Version information

• RDK: v1.4
• Robot software: v3.6

Describe the bug
Robot::busy() seems to be not be updated to actual state of the robot after calling Robot.ExecutePlan(). When running the example basics4_plan_execution.py, it doesn't print anything unless there is a time.sleep(...) between the call of Robot.ExecutePlan() and Robot::busy().

Additional context
"I tested various values for time.sleep() and found that Robot::busy() returned False with a delay of 0.121 seconds, but returned True with a delay of 0.122 seconds or more."

[pzhu-flexiv]

@isa-9 After a plan/primitive command is sent to the robot, it takes some time for the robot to load the command and compute trajectory before actually start executing. During this preparation period (varies from 10ms to 200ms depends on the complexity of the command and trajectory computation), Robot::busy() will return false because the execution is not started yet.

We used to have forced 200ms wait in ExecutePlan() and ExecutePrimitive(), but it did not turn out to be an optimal solution as some customers want short-blocking function calls. Thus, we removed the forced wait, and gave the flexibility back to the user.

We will add an input parameter block_until_started to ExecutePlan() and ExecutePrimitive() to let user decide whether they want these functions to return immediately or return after the preparation period is finished.