9.0 -> 9.1 upgrade procedure is not clear and not production ready

[Timur Nurlygayanov]

Summary:
1) We don't have the "push the button" procedure for update from MOS 9.0 to MOS 9.1
2) We don't have the proper documentation about the update from MOS 9.0 up to MOS 9.1 and "how user can update MOS 9.0 environment to MOS 9.1 environment"
3) We don't have the proper way to verify that we installed MOS 9.1 with all required updates now. You can just trust to the documentation and believe that MOS installed the fresh version of the packages, but we don't know the "exact" and documented steps for the verification that all updates were installed correctly.

QA team created the documentation "how to update MOS 9.0 to MOS 9.1" but it doesn't work because of the following blocker issues:
https://bugs.launchpad.net/fuel/+bug/1620301
https://bugs.launchpad.net/fuel/+bug/1620526

So, we have only documentation which was created by QA team and we asked several times to prepare the clear documentation about the update procedure - how to upgrade the environment, how to verify which version of the MOS is installed on the environment and etc.

As a customer I should have the clear documentation with the very easy steps for upgrades and this documentation should have 1-3 steps like "run the command" or "run the script", without any Linux magic and worakarounds (without any non-documentated required steps).

Note:
We use this doc for update now (but it doesn\t work, please see "Known Issues" section):
https://mirantis.jira.com/wiki/display/QA/MOS+9.1+installation

The priority is Critical because the issue is blocker for all MOs 9.1-related QA activities like bugs verification / acceptance testing.

[Olena Logvinova (ologvinova)]

Fix proposed to branch: master
Review: https://review.fuel-infra.org/#/c/26111

[Timur Nurlygayanov (tnurlygayanov)]

The status is "In Progress" because the commit is still on review now and we have some comments from reviewers.

[Olena Logvinova (ologvinova)]

Fix merged to branch: master
Review: https://review.fuel-infra.org/#/c/26111

[Olena Logvinova (ologvinova)]

The instruction is published at https://docs.mirantis.com/openstack/fuel/fuel-master/operations/update-from-9-to-9-1.html.