volume/rbd-backend: add a unit test
volume/rbd-backend: add a unit test

redhat-cip/puppet-openstack-cloud,redhat-cip/puppet-openstack-cloud,gwdg/puppet-openstack-cloud,gwdg/puppet-openstack-cloud,gwdg/puppet-openstack-cloud,Prophidys/puppet-openstack-cloud,goneri/puppet-openstack-cloud,Prophidys/puppet-openstack-cloud,gwdg/puppet-openstack-cloud,goneri/puppet-openstack-cloud,redhat-cip/puppet-openstack-cloud,Prophidys/puppet-openstack-cloud