standardized aws_secret_key, aws_access_key, region parameters

Also did some other standardization/cleanup such as moving boto imports
into a try/except statement, making sure not to log aws_secret_key, etc.
fixed doc bug
Merged with 8171b7ba48d701846aabf1982592703beee0aabb
more cleanup to standardize comments, region/ec2_url handling
Added aliases to aws_access_key description
Merge branch 'aws_param_cleanup_2' of github.com:bpennypacker/ansible into aws_param_cleanup_2