Add command output tests for "job create", "job killall", "job kill"

Add tests to ensure that IO behavior of client commands is correct.

Improve IO behavior in the IO client, so that users get more information.
Formorely, many commands succeeded silently, when it would be more helpful to actually tell the user that you did something. (This shouldn't affect scripting, because in these commands, the only result that's needed by a scripter is succeess/failure, which is carried by the exit code.)

Bugs closed: aurora-645

Reviewed at https://reviews.apache.org/r/24852/