Update list of remote branches.

Do this before listing the branches for which we will build venvs
so that we pick up on new branches.

Change-Id: Ifb53a923902008594f93c693be499af5d7bd821b

slave_scripts/build-venv.sh

@@ -8,6 +8,9 @@ export PIP_DOWNLOAD_CACHE=~/cache/pip
 rm -fr jenkins_venvs
 mkdir -p jenkins_venvs
 
+# Update the list of remote refs to pick up new branches
+git remote update
+
 # Build a venv for every known branch
 for branch in `git branch -r |grep "origin/"|grep -v HEAD|sed "s/origin\///"`
 do