get project ID in Keystone v3 client

[c-mart]

Apparently Cinder client no longer has a client.client.auth_ref['token']['tenant']['id']:

root@tombstone01-utility-container-80089f8a:~/cinderback# python cinderback.py --os-tenant-name demo backup
INFO: Starting Volumes Backup
INFO: Processing 27GB from volume  (id: dad83807-1b76-4549-a3c2-5394b028be0e)
Traceback (most recent call last):
  File "cinderback.py", line 905, in <module>
    main(args)
  File "cinderback.py", line 864, in main
    keep_only=args.keep_only)
  File "cinderback.py", line 422, in backup_all
    tenant_client = self.get_client(owner_tenant_id, keep_tenant)
  File "cinderback.py", line 783, in get_client
    self.client.client.auth_ref['token']['tenant']['id']
TypeError: 'AccessInfoV3' object has no attribute '__getitem__'

Instead we now have a client.client.auth_ref.project_id.

[c-mart]

Closing in favor of #5.