plugins.py: Reduce default number of threads to 1

Bug: Issue 12890
Change-Id: Ifa7135677766429202561e606cb5406d298e0b27
diff --git a/tools/plugins.py b/tools/plugins.py
index 5bb122c..7b7dea7 100644
--- a/tools/plugins.py
+++ b/tools/plugins.py
@@ -139,9 +139,9 @@
             "-t",
             "--threads",
             dest="threads",
-            default=2,
+            default=1,
             type=int,
-            help="number of threads fetching data from Gerrit concurrently",
+            help="number of threads to fetch data from Gerrit concurrently",
         )
         return parser.parse_args()