library/ec2:

- use boto instead of euca2ools
- improve error handling/propagation for run failures
- rename keypair to key_name (and preserve alias for old playbooks)
- should be 100% backward compatible with the euca2ools version
use connect_ec2_endpoint instead of connect_euca, and properly pass keys to connect_ec2
Fail gracefully if boto is not available and add me to the author line.