cli::command: wrap usage errors in a UsageError

So we can distinguish them and show usage output
conditionally.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/bin/backup-client.rs

@@ -146,7 +146,9 @@ fn main() {
 
     if let Err(err) = run_cli_command(&cmd_def.into()) {
         eprintln!("Error: {}", err);
-        print_cli_usage();
+        if err.downcast::<UsageError>().is_ok() {
+            print_cli_usage();
+        }
         std::process::exit(-1);
     }