Small time step size when using CheckPointTimeLoop

When using the CheckPointTimeLoop it may happen that the last time step is extremely small (e.g. in the range of 1.0e-16), see the exercise_1p_c of the dumux-course in the exercise-mainfile folder. The reason for this are rounding errors and the implementation of the function

bool finished() const
{ return finished_ || time_ >= endTime_; }

where time_ >= endTime is false since time_ = endTime_ - eps. It would be better to use Dune::FloatCmp::eq instead. The same also holds for the function willBeFinished().