Replace httpGet with exec for readiness and liveness probe

There have been quite a few issue for using httpGet for both Probe
keep showing unreasonable timeout

net/http: request canceled (Client.Timeout exceeded while awaiting headers)

After some investigation, I switched to exec with no issue

readinessProbe:
#    httpGet:
#      path: "/_node/ready"
#      port: 9600
    exec:
      command:
        - "curl"
        - "--fail"
        - "http://localhost:9600/_node/ready"