ceph: Avoid invalid execution state
ceph: Avoid invalid execution state

security issues identified by TrailOfBits:

Improperly handled type assertion error could result in invalid
execution state.
If we obtain an error trying to get a Node object is better not
continue executing this function.

Resolves #4567

Signed-off-by: Juan Miguel Olmo Martínez <b865a88887717e9493a6b0afe813700ce1780411@redhat.com>

rook/rook,rook/nfs,rook/rook,rook/nfs,rook/nfs,rook/rook,rook/rook,rook/rook