Add default region inherited by other cookbooks.

- Allow all regions to be set by 1 attribute (but still be able to be
  overridden)
- Set default['openstack']['region'] to RegionOne

Change-Id: I15254d22bde3e2ae1291e8b37ce61f2b1d002440
Addresses: blueprint uniform-region
Merge "Add default region inherited by other cookbooks."