Add new Keystone upgrade logic

Draft preparation for rolling upgrade :---- https://etherpad.openstack.org/p/ks-upgrade

Nowdays there is a big reason why enterprises fail to gain the full
advantage of their OpenStack cloud. Upgrade has never been easy and
in many environments upgrade require extended downtime for both the
control and dataplane, which is an inherently un-cloudy characteristic
of the OpenStack platform. So fixing upgrades would increase adoptation
rate of OpenStack. Being the Identity Service of OpenStack, keystone
play very crusial role in every operation of services. Manual upgrade of
any service is very complex. So with the help of kolla-ansible we will
easily upgrade keystone.

Use Cases
--------------
1-As a Cloud Operator, I want to experience a stable, regularly
  upgraded keystone in order to utilize new features, bug fixes
  and security enhancements, so that my cloud development
  experience is consistently be more enhanced.
2-As a Cloud Operator, I want to provide my users a reliable and available
  authentication so that they do not experience any downtime.
4-As a Cloud Operator, I want to be able to roll back the most recent cloud
  upgrade I initiate in the event of issues so that I can be confident that
  even in the case of errors I will still avoid any downtime.
5-As a Cloud Operator, I want to be able to define characteristics of a
  rolling reboot of my data and control plane hosts so that my users are not
  impacted by a rolling upgrade.
6-As a Cloud Operator, I want to be able to run pre-upgrade tests to ensure
  my cloud is capable of upgrading to a specified version so that I can be
  confident in the success of my upgrade.
7-As a Cloud Operator, I want a way to validate whether an upgrade completed
  successfully, and get clear indication for any issues and how to resolve
  them with specific actions (such as repair, fix and retry, rollback).
8-As a Cloud Operator I want to know beforehand the upgrade plan including
  timing, dependencies, and which services would be impacted.

Proposed Change
--------------------------

Need to write some new task on this file : https://github.com/openstack/kolla-ansible/blob/master/ansible/roles/keystone/tasks/bootstrap_service.yml

Need to write playbook which will run on 1st controller node only as keystone services run on controller nodes, play book will mainly contains task as mentioned in step 1 to 7 in http://docs.openstack.org/developer/keystone/upgrading.html#upgrading-without-downtime

This time we need to add 0 downtime specific command logic in bootstrap_service.yml:-

keystone-manage db_sync --expand
keystone-manage db_sync --migrate
keystone-manage db_sync --contract

Implement Keystone zero-downtime upgrade
  https://review.openstack.org/#/c/405215

Gerrit topic: https://review.openstack.org/#q,topic:bp/ks-rolling-upgrade-role,n,z

Addressed by: https://review.openstack.org/425446
    Implement Keystone zero-downtime upgrade

Addressed by: https://review.openstack.org/480081
    [WIP] Implement Keystone zero-downtime upgrade

Addressed by: https://review.openstack.org/482863
    Ansible strategy for Rolling upgrade

Addressed by: https://review.openstack.org/407922
    Apply neutron database migration

Gerrit topic: https://review.openstack.org/#q,topic:bp/apply-service-upgrade-procedure,n,z