When migrating from a cluster with no MDS nodes deployed,
`{{ cephfs_data_pool.name }}` doesn't exist so we need to create a pool
for storing nfs export objects.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1950403



Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>
(cherry picked from commit bb7d37fb)