Make the Ceph operator more cautious about when it decides to remove
nodes from the Rook-Ceph cluster which are acting as osd hosts.

When `useAllNodes` is set to `true` we assume that the user wants to
have the most hands-off experience. Node removals are allowed when a
node is delted from Kubernetes and when a node has its taints/affinities
modified by the user (but not by automatic k8s modification as much as
possible).

When `useAllnodes` is set to `false` the only time a node is removed is
if it is removed from the Ceph cluster definition.
Signed-off-by: Blaine Gardner <blaine.gardner@suse.com>