title: passing arguments on aws Data Pipeline
body: <p>have anyone had any experience with Data Pipeline?</p>
  
  <p>I have been trying to find out if there is a way to pass arguments between activities in a Pipeline. unfortunately aws documentation is not very helpful on these issues...
  lets say i have a ShellCommandActivity and an EmrActivity.
  i would like to get a string from my ShellCommandActivity that i can use later as an argument for my EmrActivity (lets say a file name or an s3 path) 
  or maybe for other objects in the pipeline - for example a DataNode</p>
  
  <p>any help would be much appreciated</p>