Revert "Temporarily stop booting nodes in citycloud-kna1"

This reverts commit a7edbb7a18.

Merge once the mirror server in citycloud-kna1 is reachable and
working correctly.

Change-Id: I72c8344d60a3f6fe184b1ffc8a64c8f8a8d78c80

nodepool/nl02.openstack.org.yaml

@@ -197,7 +197,7 @@ providers:
     pools:
       - name: main
         # Canary capacity (by memory less than half capacity of airship pool).
-        max-servers: 0
+        max-servers: 10
         labels:
           - name: centos-7
             min-ram: 8000
@@ -269,7 +269,7 @@ providers:
       - name: airship
         # Jobs expected to run 1x 32GB instance + 3x 16GB instances with
         # goal of running 4 jobs concurrently.
-        max-servers: 0
+        max-servers: 16
         labels:
           - name: ubuntu-bionic-expanded
             min-ram: 16000