Misnamed param for setup_test_volume

[Mark T. Voelker]

When setting up the iSCSI backend, we also call the
setup_test_volume class from puppet-cinder. It takes a param
called 'volume_name', but we're trying to send it 'volume_group':

https://github.com/CiscoSystems/puppet_openstack_builder/blob/h.1/data/hiera_data/cinder_backend/iscsi.yaml#L2

https://github.com/CiscoSystems/puppet-cinder/blob/h.1/manifests/setup_test_volume.pp#L17

The bug has no negative effect since the value we set matches
the default value for volume_name anyway, but users that read
the YAML will probably be confused if they try to change the
volume name and don't see it take effect.

[Mark T. Voelker (mvoelker)]

Fix here:
https://review.openstack.org/#/c/75996/