At present, when a cluster is patched without node_count (e.g. when
health_status and health_status_reason are patched), the node_count in
the cluster_update invocation contains cluster.node_count instead of
default_ng_worker.node_count which causes unexpected behaviour when a
cluster has additional nodegroups (e.g. the default-worker size gets
incremented by 1 if the additional nodegroup has 1 worker each time the
cluster is patched).
This PS fixes this issue by using default_ng_worker.node_count if path
"/node_count" is not present in the patch object.
Story: 2005266
Task: 39962
Change-Id: I0df5149860604f0adf52701df371e34a6e667b9d
55fd12a47c