Allow a new argument, "build", to be passed through a task to get just the output of the built files.

This allows built files to be handled differently than just running phantom, and even moved to a more convenient spot. 

Here is an example SH file that would work with this process (where "all" is the task options in the Gruntfile.js).

    '''
    #!/bin/sh
    myvar=$(echo $(grunt qunit-serverless:all:build) | awk '{print $5}')
    echo $myvar
    ''''