If threshold is very large, for example, 21474836480, it would get
printed using scientific notation. If that expression was then used
to recreate the AlarmSubExpression, it would fail because the parser
didn't handle scientific notation.
So, instead use DecimalFormat to ensure a valid decimal number without
scientific notation. This then limits the threshold to 15 decimal
places, but that should be enough. It would be better to have no limit
but I have not been able to find a way to do that.
Change-Id: I0511bd73a0ab65498dd615d8f5049b5663720b6a
d3354d10ef