netCDF long_name for loc, shp and scale variables

[wcarthur]

The long_name attribute for the location, shape and scale variables (loc, shp and scale respectively) is hard coded to be "Location parameter for GEV distribution", irrespective of the actual distribution used for estimating ARI values.

This should be set to match the configuration setting in the Hazard -- ExtremeValueDistribution option.

See the HazardCalculator.saveHazard() method in hazard/__init__.py.
The EVD is already an attribute of HazardCalculator class, so should be simple as formatting self.evd in the string that defines the long_name attribute in the netcdf file