Replace grafana home dashboard with file in node_custom_config folder.

Change-Id: I00e3963ee287c526935e34169b63b1a40e6b4025

Ansible task support vars directive, no need implement another one in
merge_config. This patch remove the vars directive in merge_config
action plugin.

Change-Id: I33648a2b6e39b4d49ce76eb66fbf2522721f8c68

Change-Id: I672d6fea935cbe7416ebd0cfff5006fddb9cd534
Partially-implements: blueprint better-reconfigure

Added ansible role to deploy grafana

Added host group for grafana deployment

Co-Authored-By: zhubingbing <zhubingbing10@gmail.com>

Change-Id: I3dec4e8586b6f65fa7de66a48506d1c79de2fe1e
Partially-Implements: Blueprint performance-monitoring