High available for ovn db

OVN support clustered database. If want to use high-available database in kube-ovn,
modify ovn-central deployment in yamls/ovn.yaml.

Change the replicas to 3, and add NODE_IPS environment var points to node that has label kube-ovn/role: "master".

  1.       replicas: 3
  2.       containers:
  3.         - name: ovn-central
  4.           image: "index.alauda.cn/alaudak8s/kube-ovn-db:v1.0.1"
  5.           imagePullPolicy: Always
  6.           env:
  7.             - name: POD_IP
  8.               valueFrom:
  9.                 fieldRef:
  10.                   fieldPath: status.podIP
  11.             - name: NODE_IPS
  12.               value: 192.168.55.10, 192.168.55.11, 192.168.55.12
  1. ovn-central-fbdbd9d4d-jv8cr            1/1       Running   0          19h      # waiting to become a leader
  2. ovn-central-fbdbd9d4d-pgvhl            1/1       Running   0          19h      # waiting to become a leader
  3. ovn-central-fbdbd9d4d-rk2c7            1/1       Running   0          19h      # the leader now

More detail about ovsdb cluster mode please refer to this link