ostree/config: Check for too many args

Currently it's not an error to provide too many arguments to an ostree
config command. Change it so we print usage information in that case,
and update the unit tests.

Closes: #1743
Approved by: cgwalters

src/ostree/ot-builtin-config.c

@@ -71,6 +71,7 @@ ostree_builtin_config (int argc, char **argv, OstreeCommandInvocation *invocatio
   g_autofree char *section = NULL;
   g_autofree char *key = NULL;
   g_autoptr(GKeyFile) config = NULL;
+  int correct_argc;
 
   context = g_option_context_new ("(get KEY|set KEY VALUE|unset KEY)");
 
@@ -85,6 +86,17 @@ ostree_builtin_config (int argc, char **argv, OstreeCommandInvocation *invocatio
 
   op = argv[1];
 
+  if (!strcmp (op, "set"))
+    correct_argc = 4;
+  else
+    correct_argc = 3;
+
+  if (argc > correct_argc)
+    {
+      ot_util_usage_error (context, "Too many arguments given", error);
+      return FALSE;
+    }
+
   if (!strcmp (op, "set"))
     {
       if (opt_group)