Try booting nodes in Rackspace Flex

Our expected Nodepool images are present in the raxflex-sjc3
provider now, so raise max-servers to 1 in order to get some sample
builds we can analyze for obvious issues like connectivity.

Depend on the subnet resizing change since that might otherwise be
disruptive if it deployed while jobs are running there.

Depends-On: https://review.opendev.org/927813
Change-Id: If8b39b53608188e5881a273e6d092981a5871e84

nodepool/nl01.opendev.org.yaml

@@ -183,7 +183,7 @@ providers:
     diskimages: *provider_diskimages
     pools:
       - name: main
-        max-servers: 0
+        max-servers: 1
         labels:
           - name: centos-9-stream
             flavor-name: 'gp.0.4.8'