test_nova.sh uses old cirros images

Update test_nova.sh to download Cirros 0.3.1 for config_drive support,
and for consistency with the other Cirros image downloads within this
module.

Change-Id: Ic022c0199d254c3cadb08ccda1ef588fd3f09c35
Closes-Bug: #1275746
Merge git://github.com/puppetlabs/puppetlabs-openstack