Corrected spelling error that was preventing the propagate_at_launch attribute from being set properly in Eucalyptus, and presumably in AWS too.
Unit test for autoscaling tags, and specific test for setting propagate_at_launch in endElement.
Merge pull request #1739 from jpommer/as_tags_propagation_fix

Corrected spelling error that was preventing the propagate_at_launch attribute. Fixes #1739.