[misc][plugin] improve log messages (#10386)

Signed-off-by: youkaichao <youkaichao@gmail.com>

vllm/plugins/__init__.py

@@ -27,6 +27,9 @@ def load_general_plugins():
     allowed_plugins = envs.VLLM_PLUGINS
 
     discovered_plugins = entry_points(group='vllm.general_plugins')
+    if len(discovered_plugins) == 0:
+        logger.info("No plugins found.")
+        return
     logger.info("Available plugins:")
     for plugin in discovered_plugins:
         logger.info("name=%s, value=%s, group=%s", plugin.name, plugin.value,