Adjust to non-deprecated names in Keyring 1.6.+

Keyring 1.1 moved the concrete backend implementations into their
own modules. As we depend on 1.6.1+, we can make use of the new
name and remove the old one without deprecation-fallback.

Change-Id: I0682b13fc9f488b3f3d9fd057f712909fcd48bc4
Do lookups for user, project in volume create

This required https://review.openstack.org/26323 in keystoneclient,
merged long ago...

Also adds some tests for 'volume create'

Change-Id: I55bededbc20b5dcf2833c59eb2b6b069703d8a9a