don't print help message for usage errors

Don't print potentially verbose help messages in case of usage errors,
but print only the usage error followed by a pointer to the command's
help.  This aligns with Docker.

```
$ podman run -h
flag needs an argument: -h
See 'podman run --help'.
```

Signed-off-by: Valentin Rothberg <vrothberg@suse.com>

Closes: #1379
Approved by: rhatdan

cmd/podman/main.go

@@ -51,6 +51,7 @@ func main() {
 	app := cli.NewApp()
 	app.Name = "podman"
 	app.Usage = "manage pods and images"
+	app.OnUsageError = usageErrorHandler
 
 	app.Version = version.Version