push-all: Use TOR_UPSTREAM_REMOTE_NAME to override UPSTREAM_BRANCH

We already allow this override in our pre-push hook, so let's allow
it here too.

(I call my upstream branches "origin")

scripts/git/git-push-all.sh

@@ -1,9 +1,9 @@
 #!/bin/bash
 
 # The remote upstream branch on which git.torproject.org/tor.git points to.
-UPSTREAM_BRANCH="upstream"
+UPSTREAM_BRANCH=${TOR_UPSTREAM_REMOTE_NAME:-"upstream"}
 
-git push $UPSTREAM_BRANCH \
+git push "$UPSTREAM_BRANCH" \
    master \
    {release,maint}-0.4.1 \
    {release,maint}-0.4.0 \