Correct `puppet module list` check in beaker
Correct `puppet module list` check in beaker

The final check during the prep stage, where `puppet module list` is
run so that its output can be used for debugging, should run on the
current host in the loop, not the first host in the array.

Change-Id: I8335f05ad2eec6d0e534299895b14497ab213c33

rdo-puppet-modules/puppet-gnocchi,openstack/puppet-gnocchi,openstack/puppet-gnocchi