Use correct variable for tenant_name
Use correct variable for tenant_name

- terraform also uses `tenant_name` for
  keystone V3

[#119565681](https://www.pivotaltracker.com/story/show/119565681)

cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release,cloudfoundry-incubator/bosh-openstack-cpi-release