[WFLY-1907] / [WFLY-490] The whoami operation needed the reply type setting so that it would be represented correctly in the JMX facade.

This commit now sets the return type to String, although previously no return type had been specified clients have been identified that are dependent on the return type being a String.
[WFLY-430] / [WFLY-490] Update the whoami operation so that it outputs the mapped roles for the current user if verbose=true and the current access control provider supports role mapping.