Use NaN for missing warning/crit threshold values

Handle loading the Warning and Critical threshold interfaces like the
hard/soft shutdown ones and use NaN if a low or high value is missing in
the JSON, assuming the other one is there.

Using NaN means the threshold alarm will never be tripped for that
property.

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: Ib6b6d3a657df8e77ea4c7e5a491ea367693c5951
1 file changed