Add an enable_cinder_backend_quobyte option to etc/kolla/globals.yml to
enable use the Quobyte Cinder backend.
Change the bind mounts for /var/lib/nova/mnt to include the shared
propogation if Quobyte is enabled.
Update the documentation to include a section on configuring the Cinder.

Implements: blueprint cinder-quobyte-backend

Change-Id: I364939407ad244fe81cea40f880effdbcaa8a20d