pybind/cephfs, mgr/volumes: refactor purge() to be non-recursive

pybind/cephfs, mgr/volumes: refactor purge() to be non-recursive

Method purge() in trash.py calls rmtree() which is recursive method. To
avoid Python's recurision limit, switch to non-recursive approach.

Path to directory along directory handle are clubbed in to a tuple and
that tuple is stored on the stack. Storing directory handle reduces call
to opendir() dramatically.

Fixes: https://tracker.ceph.com/issues/71648
Signed-off-by: Rishabh Dave <ridave@redhat.com>