Disable the osuosl arm64 cloud

This is a temporary measure while we convince the mirror in that region
to start a working afs client. For some reason (perhaps related to
volume slowness, cache corruption, of the local dkms build) we have not
been able to successfully start the openafs client here.

Change-Id: Id5de5ec46f1c98ca2c64b6e2f61e8ce73dfbf83d

nodepool/nl03.opendev.org.yaml

@@ -474,7 +474,7 @@ providers:
         config-drive: true
     pools:
       - name: main
-        max-servers: 15
+        max-servers: 0
         labels:
           - name: centos-8-arm64
             min-ram: 8000