Fix GetClusterSize to return actual size in line with the rest of CSR
Fix GetClusterSize to return actual size in line with the rest of CSR

It returned the number of registered nodes, but should return the number
of provisioned nodes instead.

mmerrill3/autoscaler,kubernetes/autoscaler,kubernetes/autoscaler,bskiba/autoscaler,bskiba/autoscaler,kubernetes/autoscaler,mmerrill3/autoscaler,mmerrill3/autoscaler,kubernetes/autoscaler,mmerrill3/autoscaler,bskiba/autoscaler