Command does not output anything, let's add a formatter.row call.
We should include the possible outputs in the help text.
Further improvement possibility. This command can be used for checking if the compaction is done but very impractical if one wants to wait until it is done. Wish there would be a flag in the shell that enforces synchronous compactions, that is, every time you issue a compact or major_compact in the shell while this flag is set, you won't get back the prompt until it finishes.