Disable pretty json printing for system metrics

Prior to this commit, the system metrics were pretty printed. This leads
to additional consumed disk space. The json2timeseries STDIN expects
that all data incoming is a single line. This commit changes the system
metrics to log minified JSON.

Author: Jarret Lavallee

files/system_metrics

@@ -325,7 +325,7 @@ module SystemMetrics
       hostkey = @hostname.gsub('.', '-')
       metrics_json = {'timestamp' => @time_stamp_obj.utc.iso8601, 'servers' => {}}
       metrics_json['servers'][hostkey] = {@metric_type => metrics_data}
-      JSON.pretty_generate(metrics_json)
+      JSON.generate(metrics_json)
     end
 
     # Create the metric file and put the json data in it