Utilise ['openstack']['region'] from cookbook-openstack-common

- Set ['openstack']['network']['region'] to equal ['openstack']['region']
- Add test to override the endpoint region and confirm it is used

Change-Id: I68463f8cad7c424115ad75a39068c880ad3d3ef9
Addresses: blueprint uniform-region
Merge "Utilise ['openstack']['region'] from cookbook-openstack-common"