buildvm: Try and fix s390x sshfs mounts

Because of the when we had here before it would try and do a nfs mount
on the runroot s390x builders, but that will completely fail, as they
are not in the same datacenter. Instead try and exclude them here so
they can get the sshfs mount later.

Signed-off-by: Kevin Fenzi <kevin@scrye.com>

playbooks/groups/buildvm.yml

@@ -26,7 +26,7 @@
         role: nfs/client,
         mnt_dir: "/mnt/fedora_koji",
         nfs_src_dir: "{{ koji_hub_nfs }}",
-        when: "env == 'staging' or createrepo or 'runroot' in group_names",
+        when: "env == 'staging' or createrepo or 'runroot' in group_names and not inventory_hostname.startswith('buildvm-s390x')",
       }
     - role: nfs/client
       mnt_dir: '/mnt/koji/ostree'