ceph: operator should only "watch" OSD placement nodes
ceph: operator should only "watch" OSD placement nodes

This change is the first part to improve the watch OSD nodes logic in
the Rook Ceph operator.
This commit changes the "is node valid check" to use the OSD placement
instead of the all placement. The OSD placement is "merged" with the
all placement already.

Second step will be to skip the first "iteration" of the "nodes added"
events and then start the actual watch logic.

Partially resolves #6111.

Signed-off-by: Alexander Trost <88b6b84d9fa0dbf878e34ae3d402bc4895fcd37e@googlemail.com>

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