qga: return a more explicit error on why a command is disabled

qmp_disable_command() now takes an optional error string to return a
more explicit error message.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1928806

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
*fix up 80+ char line
Signed-off-by: Michael Roth <michael.roth@amd.com>

qga/main.c

@@ -375,7 +375,7 @@ static void ga_disable_non_whitelisted(const QmpCommand *cmd, void *opaque)
     }
     if (!whitelisted) {
         g_debug("disabling command: %s", name);
-        qmp_disable_command(&ga_commands, name);
+        qmp_disable_command(&ga_commands, name, "the agent is in frozen state");
     }
 }
 
@@ -1328,7 +1328,7 @@ static GAState *initialize_agent(GAConfig *config, int socket_activation)
         s->blacklist = config->blacklist;
         do {
             g_debug("disabling command: %s", (char *)l->data);
-            qmp_disable_command(&ga_commands, l->data);
+            qmp_disable_command(&ga_commands, l->data, NULL);
             l = g_list_next(l);
         } while (l);
     }