add test cases to test add and delete node taints
mock functions:
kubernetes.config.load_kube_config
kubernetes.client.CoreV1Api.read_node
kubernetes.client.CoreV1Api.patch_node
mock functions above has been tested on a real kubernetes cluster,
which ensure mock functions have the same behaviors with kubernetes
apis.
Story: 2002843
Task: 24909
Change-Id: I12d2a15404afc38274aaa87841a63ee576aaf095
Signed-off-by: SidneyAn <ran1.an@intel.com>