Set airship-citycloud max-servers to 0

We've been notified that these resources won't be provided any longer.
This is the first step of setting max-servers to 0 and removing images
from the cloud. Once that is in we can remove the cloud more completely.

Change-Id: Iabcd6487a5bb3ed7fb6aae5dadf23a8171abcb7f

nodepool/nl02.opendev.org.yaml

@@ -191,7 +191,7 @@ providers:
     pools:
       - name: main
         # Canary capacity (by memory less than half capacity of airship pool).
-        max-servers: 10
+        max-servers: 0
         labels:
           - name: centos-7
             min-ram: 8000
@@ -253,7 +253,7 @@ providers:
       - name: airship
         # Jobs expected to run 1x 32GB instance + 3x 16GB instances with
         # goal of running 4 jobs concurrently.
-        max-servers: 16
+        max-servers: 0
         labels:
           - name: ubuntu-bionic-expanded
             min-ram: 16000

nodepool/nodepool.yaml

@@ -96,7 +96,7 @@ providers:
     region-name: 'Kna1'
     cloud: airship-citycloud
     rate: 0.25
-    diskimages: *provider_diskimages
+    diskimages: []
 
   - name: inmotion-iad3
     region-name: 'iad3'