fleetctl: Need return fail if no args given to some subcommand.

[wuqixuan]

Some subcommand like destroy/load/start/status/stop/submit/unload,
need to give prompt if no args for them.
Add the same prompt "One unit file must be provided" as the "cat"
subcommand is doing:
[root@localhost fleet-0.10.1]# fleetctl cat
One unit file must be provided

[wuqixuan]

Before the code, destroy/load/start/status/stop/submit/unload subcommand without any args will give 0 return value. It should return error code, like -1 as "cat" is doing now. That's why to add those codes.

[scole-scea]

Maybe: "At least one unit file must be specified."

[wuqixuan]

Currently, "cat" subcommand give "One unit file must be provided". So other subcommand I gave the same.

[scole-scea]

Yes, the cat subcommand does say "one". However, the cat subcommand only takes one unit as an argument.

destroy/load/start/status/stop/submit/unload all take one or more units as arguments.

[wuqixuan]

So I think we need modify the message of "cat", instead.

[scole-scea]

Well, cat has a different command-line interface. There's no reason it's error messages shouldn't reflect that difference.

[bcwaldon]

One or more unit files must be provided

[wuqixuan]

@bcwaldon, are all commands or just stop need not give error if no args failing ?
If all commands, then "cat" code need remove the check?

func runCatUnit(args []string) (exit int) {
    if len(args) != 1 {
        stderr("One unit file must be provided")
        return 1
    }

Or some need check, some need not check ? 

[mischief]

@wuqixuan please update the messages as @bcwaldon asked and then lgtm.

[wuqixuan]

@mischief, actually I don't know what @bcwaldon exact suggestions are.
Which commands are idempotent without checking, while which need to be checked ?