repo_pull: Add missing import

Change-Id: Ieaeb8524e9543ecb962236c009e62f6b8d89ffaf
diff --git a/tools/repo_pull/repo_patch.py b/tools/repo_pull/repo_patch.py
index e2a0453..c5367ca 100755
--- a/tools/repo_pull/repo_patch.py
+++ b/tools/repo_pull/repo_patch.py
@@ -23,6 +23,7 @@
 
 import argparse
 import os
+import sys
 
 from gerrit import (
     create_url_opener_from_args, find_gerrit_name, query_change_lists, get_patch