Fix e2e flag test

Signed-off-by: Tim Vaillancourt <tim@timvaillancourt.com>

Author: timvaillancourt

go/flags/endtoend/vttablet.txt

@@ -809,6 +809,8 @@ Usage of vttablet:
 	YAML file config for tablet
   --tablet_dir string
 	The directory within the vtdataroot to store vttablet/mysql files. Defaults to being generated by the tablet uid.
+  --tablet_discovery_concurrency int
+	concurrent tablet discoveries (default 1024)
   --tablet_filters value
 	Specifies a comma-separated list of 'keyspace|shard_name or keyrange' values to filter the tablets to watch
   --tablet_grpc_ca string