Protect against missing fields in rackspace endpoint documents

In a specific case a rackspace api endpoint returned no region key

'{"tenantId"=>"654557", "publicURL"=>"https://backup.api.rackspacecloud.com/v1.0/654557"}'

As a guard against this case, this commit sets the region to be global
should it not be defined in the endpoint hash
Merge pull request #2043 from bfosberry/master

Protect against missing fields in rackspace endpoint documents