Make osc-tox-unit-tips work on other repos

We want to run osc-tox-unit-tips on changes to os-client-config and
python-openstacksdk - but the tox role defaults to using
zuul.project.src_dir as the working directory. We want it to always be
the openstackclient source dir.

Change-Id: Ic7a49b79fb9141d9d0b8da40e10c85b107564edc

Author: emonty

.zuul.yaml

@@ -17,6 +17,9 @@
       - openstack/python-openstacksdk
     vars:
       tox_envlist: unit-tips
+      # Set work dir to openstackclient so that if it's triggered by one of the
+      # other repos the tests will run in the same place
+      zuul_work_dir: src/git.openstack.org/openstack/python-openstackclient
 
 - job:
     name: osc-functional-devstack-base