uses patch() instead of update()

[aaronlevy]

It's possible that new versions of kubernetes introduce new fields in objects (e.g. "taints" on node objects in v1.6). If we use update() rather than patch() we possibly will clear these fields inadvertently if our client-go is not up-to-date enough to know about the new fields.

Discussion of running into this issue with flannel: https://github.com/coreos/flannel/issues/667#issuecomment-293150531