Fix publishlang

publishlang calls a script that uses tox again, with recent CI changes
tox is not always available in PATH.

Set ensure_global_symlinks so that tox is in PATH.

Change-Id: Ib30c5af58564425d7bd2c9cd7118423c4ce643d9

.zuul.yaml

@@ -43,6 +43,7 @@
       Build translated manuals using "publishlang" tox environment.
     vars:
       tox_envlist: publishlang
+      ensure_global_symlinks: true
     files: &files-publishlang
       - ^.*\.po$
       - ^.*\.pot$