Correct tox env parameter for horizon py27dj14.

* .../jenkins_job_builder/config/horizon.yaml: In the
gate-horizon-python27-django14 job definition, run-tox.sh was being
passed the full tox environment name of py27dj14 even though it
prepends py already. This corrects it to just 27dj14 so the correct
environment name will be constructed by the script.

Change-Id: I71e0cff7fe80d8e1e8b5cf5aec77537590c48f92
Reviewed-on: https://review.openstack.org/35157
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins