Add shorter timeout for GCP util. (#4762)

* Add shorter timeout for GCP util.

* Add comment for change reason and unit for timeout.

Author: qlzh727

official/utils/logs/cloud_lib.py

@@ -25,7 +25,10 @@
 def on_gcp():
   """Detect whether the current running environment is on GCP."""
   try:
-    response = requests.get(GCP_METADATA_URL, headers=GCP_METADATA_HEADER)
+    # Timeout in 5 seconds, in case the test environment has connectivity issue.
+    # There is not default timeout, which means it might block forever.
+    response = requests.get(
+        GCP_METADATA_URL, headers=GCP_METADATA_HEADER, timeout=5)
     return response.status_code == 200
   except requests.exceptions.RequestException:
     return False