More cli improvements

* Write usage to standard error
* Fix small formatting error with the usage information
* Add `-help` flag and suppress the exception backtrace for `UnrecognizedArgumentException`
* Add `-properties` flag to chose an arbitrary path for the AWS credentials properties file
* Avoid compiler warning/error suppression
* Don't mask the FileNotFound exception for a properties path -- we should instead handle all the exceptions `PropertiesCredentials` raises: http://docs.aws.amazon.com/AWSJavaSDK/latest/javadoc/com/amazonaws/auth/PropertiesCredentials.html