Destroy Nova resource before Neutron
Destroy Nova resource before Neutron

Net delete will fail if there are still instances on this network,
destroy the resources reversely.

Change-Id: Ib0976352ae81ac94d8b31ebaed93758ca4210ec5
Closes-bug: #1488757

dtroyer/grenade,openstack-dev/grenade,dtroyer/grenade,openstack-dev/grenade