"locations_lyr" is a new layer you are creating in the script. Your script is creating it in memory, but is not adding it to the map.
If you want it added to the map table of contents, you need to:
1. Go into the script tool properties parameters tab, and set up a derived parameter of type Feature Layer.
2. Edit the script to set the parameter value
arcpy.SetParameterAsText(0, "locations_lyr")
No RefreshActiveView should be necessary, the layer will appear the map (if you run the script tool "in process").
UPDATE: For the output to be added to the map Add Outputs To Map must be on. (In ArcMap this is found in Geoprocessing > geoprocessing settings. From the Python window, this is an environment setting.
Using geoprocessing options to control tool execution—Help | ArcGIS for Desktop
You can also turn this on and off in the geoprocessing enviroinment setting addOuyputsToMap
env—Help | ArcGIS for Desktop