Temporarily stop using citycloud-sto2
Temporarily stop using citycloud-sto2

We're getting a wide variety of job failures in citycloud-sto2, from
mirror access problems to DNS lookup timeouts, indicating their
network may be overloaded or otherwise misbehaving in that region.
Temporarily disable nodepool's use of that region so as to avoid
further failures while the provider investigates.

Change-Id: I62ef79c99f38b91fc0157f6cc9879e9e653d5718

openstack-infra/project-config,openstack-infra/project-config