feat: Add --feature-gate flag to yurt-controller-manager

[DrmagicE]

Ⅰ. Describe what this PR does

Add --feature-gates flag to yurt-controller-manager.

Reference:
https://github.com/kubernetes/kubernetes/blob/v1.16.15/cmd/kube-controller-manager/app/options/options.go#L251

Ⅱ. Does this pull request fix one issue?

fixes #212

Ⅲ. List the added test cases (unit test/integration test) if any, please explain if no tests are needed.

Ⅳ. Describe how to verify it

step1
Start a 2 nodes Kubernetes cluster, name the master node as master and the worker node as worker:

$ kubectl get nodes
NAME     STATUS   ROLES    AGE   VERSION
master   Ready    master   30h   v1.16.15
worker   Ready    <none>   30h   v1.16.15

Install and run yurt-controller-manager with the following --feature-gates flags:

./yurt-controller-manager  --kubeconfig $your-kubeconfig --feature-gates=LegacyNodeRoleBehavior=false

step2
Stop the kubelet on the worker node.

step3
Watch the output log of yurt-controller-manager and wait for the NodeNotReady event to be observed by the controller. After observing the event, if there is not showing “Entering master disruption mode”, then the --feature-gates is working as intended.

Ⅴ. Special notes for reviews

[rambohe-ch]

LGTM