Don't use --verbose with yarn

This appears to output something like 145,000 lines in our build
logs, so let's be less verbose.

Change-Id: Ie41c1f21a090de84cb51331c00668b9b7f06379a

tools/pip.sh

@@ -53,7 +53,7 @@ then
         # Be forgiving of package retrieval errors
         attempts=0
         set +e
-        until yarn install --verbose; do
+        until yarn install; do
             ((attempts++))
             if [[ $attempts > 2 ]]
             then