title: S3 checkpointing for spark streaming leads to an error
body: <p>I have enabled checkpointing for my sparkstreaming application using the getOrCreate method. The checkpoint directory points to an S3 bucket.
  The problem i have is a credential issue in accessing S3 :</p>
  
  <p>Caused by: java.lang.IllegalArgumentException: AWS Access Key ID and Secret Access Key must be specified as the username or password (respectively) of a s3 URL, or by setting the fs.s3.awsAccessKeyId or fs.s3.awsSecretAccessKey properties (respectively).</p>
  
  <p>I have already set the environment variables (AWS_SECRET_KEY and AWS_ACCESS_KEY). 
  Also my fs.s3.awsAccessKeyId or fs.s3.awsSecretAccessKey have been specified in the application.conf.. So i dont know why it still fails.</p>