tests: fix `test_nfs_is_up` test
tests: fix `test_nfs_is_up` test

the data structure seems to have been modified in ceph@master (quincy).

This commit update the test accordingly.

Signed-off-by: Guillaume Abrioux <30a9df5a0293a6108675377fa1673f7aa713f915@redhat.com>

ceph/ceph-ansible,ceph/ceph-ansible