mgr/nfs: Do not ignore clusters from rados pool conf objects

mgr/nfs: Do not ignore clusters from rados pool conf objects

Early handling of NoOrchestrator exception via a2192c73e41e prevented us
from looking for namespaces containing conf objects in .nfs pool. This
would mean that we fail to recognize such namespaces as clusters thereby
prohibiting the creation of nfs exports. We could instead search for
such namespaces while handling the NoOrchestrator exception within
available_clusters() before returning the final list of clusters.

Fixes: https://tracker.ceph.com/issues/66800
Signed-off-by: Anoop C S <anoopcs@cryptolab.net>