Made update_mirror.sh skip the existing files

bazel/update_mirror.sh

@@ -34,13 +34,18 @@ trap cleanup EXIT
 function upload {
   local file="$1"
 
+  if gsutil stat "gs://grpc-bazel-mirror/${file}" > /dev/null
+  then
+    echo "Skipping ${file}"
+  else
     echo "Downloading https://${file}"
     curl -L --fail --output "${tmpdir}/archive" "https://${file}"
 
     echo "Uploading https://${file} to https://storage.googleapis.com/grpc-bazel-mirror/${file}"
-  gsutil cp -n "${tmpdir}/archive" "gs://grpc-bazel-mirror/${file}"  # "-n" will skip existing files
+    gsutil cp "${tmpdir}/archive" "gs://grpc-bazel-mirror/${file}"
 
     rm -rf "${tmpdir}/archive"
+  fi
 }
 
 # How to check that all mirror URLs work: