Create service tenant if needed

When running the os-block-storage role on its own but no other openstack
services, cinder fails to install because the 'service' tenant is not
created for the 'cinder' user to register under.

This patch creates the service tenant like other projects do.

Change-Id: Ib3929ea363d3f97723152ed4b134be46cf2a6d21
Closes-Bug: #1306782
Merge "Create service tenant if needed"