MAGN-3238 : Number slider limits + custom node interprets slider differently than other nodes

This fix is for updating the Max / Min value in Double Slider. 

In the Double Slider : 
  if the value entered is greater than Max, then the Max value is updated to the entered value
  if the value entered is less than Min, then the Min value is updated to the entered value.
When the node is saved, these new values are saved in .dyn. 

http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-3238

- [ ]  @Steell 
Can you add a [Category("Failure")] for this test? I've decided that the fix for these tests should be in a separate PR, so for now we'll just keep track of the fact that this test is failing.