server/aws.js, details:
  - propagate options to allow option "more" propagation
  - use XS.more( options ) to set option "more"
  - ec2_describe_spot_price_history:
    - default start time to 10 days ago
    - allow source pipelet to be either regions or availability zones
    - truncate returned values to only include timestamps after start time
    - fetch additional values until value anterior to start time is retrieved
    - capture exceptions and display error with stack trace (otherwise these are captured silently)