Modify AWS components to use the the AwsConfig mixin

Modify the AWS components to all ensure the same usage of AwsConfig mixin. The latest AWS RubySDK configures the endpoint based upon the region specified in the AWS.Config(....) or the AWS:<component>.new(...)

See http://ruby.awsblog.com/post/TxVOTODBPHAEP9/Working-with-Regions for more details about working with Regions.

This PR also addresses two other small issues:
* The S3 Output plugin creation of the temp directory failing as Dir.mkdir(...) will not create directories recursively.
* If no tags are specified for an event, the format_message method will fail as it is calling .join(',') on Nil