Update barbican client usage

1. Update the code of creating a barbican client
due to its recent change.

2. Make the ‘barbican_disabled’ defaults to True as
the two barbican patches below are not
merged yet, which breaks solum gate.

  https://review.openstack.org/#/c/127313
  https://review.openstack.org/#/c/127865

3. Fix bugs for using shelve as the default key store.

Change-Id: Id5d8e125373b7dae91293bd36c46d5a5cc3a4d2b