Dynamically tune Ceph placement groups as nodes are added

[Gordon Willem Klok]

Teamster should dynamically adjust the placement group size for the cluster as new nodes are brought online (with a sufficient soak time incase of flappy nodes). See http://docs.ceph.com/docs/master/rados/operations/placement-groups/ for more information. Additionally the current config designed for very small clusters e.g. two worker nodes needs to ramp up the minimum number of written replicas for objects in the pool as the number of worker nodes increases.