Update of moderate-image sample:  - Delete file at the end of the function  - Use os and path for path/filename manipulation  - Use spawn instead of exec
Update of moderate-image sample:
 - Delete file at the end of the function
 - Use os and path for path/filename manipulation
 - Use spawn instead of exec

Change-Id: I595682f8b522ddd2594319694c8cde50451efb1d

firebase/functions-samples,firebase/functions-samples,firebase/functions-samples,firebase/functions-samples