Ensure stats file is created

Since load_raster expects to be able to rsync the statistics file that
is generated during the normalization step, we should have the
normalizer raise an error if it didn't get generated.

Refs #854

lib/gis_robot_suite/raster_normalizer.rb

@@ -79,6 +79,7 @@ def convert_8bit_to_rgb
 
     def compute_statistics
       Kernel.system("#{Settings.gdal_path}gdalinfo -mm -stats -norat -noct #{output_filepath}", exception: true)
+      raise "load-raster: #{bare_druid} gdalinfo did not create stats file" unless File.size?("#{output_filepath}.aux.xml")
     end
 
     def tmpdir