Check extension exists before calling hello route (#143)

* Check extension exists before calling hello route

* Fix formatting

Author: DarcyRaynerDD

datadog_lambda/extension.py

@@ -1,14 +1,18 @@
 import logging
 import requests
+from os import path
 
 AGENT_URL = "http://127.0.0.1:8124"
 HELLO_PATH = "/lambda/hello"
 FLUSH_PATH = "/lambda/flush"
+EXTENSION_PATH = "/opt/extensions/datadog-agent"
 
 logger = logging.getLogger(__name__)
 
 
 def is_extension_running():
+    if not path.exists(EXTENSION_PATH):
+        return False
     try:
         requests.get(AGENT_URL + HELLO_PATH)
     except Exception as e: