fdb-list (and other tools) do not print usage on missing arguments

[ChrisspyB]

Some of our tools will print the "usage" text if no arguments are given (e.g. fdb-write). fdb-list does not, even though I'm quite sure zero arguments is not a valid usage of fdb-list. An invalid argument, such as./fdb-list --madeupInvalidArgument will print the help dialogue.

It would be good if there was a properly supported --help option, and that it was printed when zero arguments are given.