Wrong initialization of stepTime in the ControlBoardDriver

[nunoguedelha]

While analyzing another issue and looking into a trace of the code executed in GazeboYarpControlBoardDriver::onUpdate, I noticed a bug in the initialization of the stepTime variable.

More precisely, the bug is in the block:

gazebo-yarp-plugins/plugins/controlboard/src/ControlBoardDriver.cpp

Lines 453 to 458 in 2839964

	//TODO: how to properly reset the initial time?
	static bool firstTime = true;
	if (firstTime) {
	firstTime = false;
	m_previousTime = _info.simTime;
	}

The first time computation should be applied to all controlboards, but is only applied to the first one (torso) because we use here a "static" variable which is static to the class method but not separately for each object.
So the computed stepTime is correct for the first updated controlboard, but wrong for the others. this issue has little or no consequence on the behavior except if we use Derivative (Kv) or Integral (Ki) gains.

I still have to check if this is true in the last commit, so I left the issue in [WIP].

CC @traversaro

[nunoguedelha]

I've checked, it's still the case in master and devel branches, actually the file didn't change since commit 2839964.

[nunoguedelha]

The fix is quite simple:
Use a flag, defined as a class property (private and non static), for initializing the simulation time to Gazebo simTime on the first call to onUpdate().

[nunoguedelha]

Fixed by #478.