Pressure units attribute in Stehekin image driver sample forcing are incorrect

[jhamman]

The pressure variable units attribute in the sample image driver forcing dataset need to be updated. From:

netcdf Stehekin_image_test.forcings_10days.1949 {
dimensions:
    time = 240 ;
    lon = 5 ;
    lat = 4 ;
variables:
...
    float pres(time, lat, lon) ;
        pres:_FillValue = 9.96921e+36f ;
        pres:long_name = "PRESSURE" ;
        pres:column = 5 ;
        pres:units = "K" ;
        pres:description = "PRESSURE" ;
...

to:

        pres:units = "Pa" ;