Fix "Enable influxdb datasource" random error

Sometimes the "Enable influxdb datasource" task failed with "503 Service
Unavailable" error. Waiting for grafana port UP seems not always enough,
it requires to wait for application ready.

Change-Id: I3a27b3086698b89a80a3f585beb810831289ae7a
Closes-Bug: #1697213

ansible/roles/grafana/tasks/post_config.yml

@@ -1,8 +1,14 @@
 ---
-- name: Wait for grafana port
-  wait_for:
-    host: "{{ api_interface_address }}"
-    port: "{{ grafana_server_port }}"
+- name: Wait for grafana application ready
+  uri:
+    url: "{{ internal_protocol }}://{{ kolla_internal_vip_address }}:{{ grafana_server_port }}"
+    status_code: 200
+  register: result
+  until: result.status == 200
+  retries: 10
+  delay: 2
+  run_once: true
+  connection: local
 
 - name: Enable influxdb datasource
   uri: