Bug 1477390

Description of problem:
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In upgrade guide for Red Hat OpenStack Platform 8, Compute nodes [1], we explicitly describe < ensure zero downtime > in section 3.4.5:

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3.4.5. Upgrading Compute Nodes

We perform the following task on each node individually to ensure zero downtime. Select a Compute node to upgrade. 

Migrate its workload. See "Migrating VMs from an Overcloud Compute Node" in the Red Hat OpenStack Platform Director Installation and Usage Guide. 
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In the same guide in different page [2], there is a sentence added 4 months ago, 

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Warning
Before performing an upgrade to the latest major version, ensure the undercloud and overcloud are updated to the latest minor versions. This includes both OpenStack Platform services and the base operating system. For the process on performing a minor version update, see "Updating the Environment" in the Red Hat OpenStack Platform 7 Director Installation and Usage guide. Performing a major version upgrade without first performing a minor version update can cause failures in the upgrade process. 
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There is a description as below in that sentence, this is linked to different content [3].

"Updating the Environment"

In that contents, there is a sentence as below. Here we explicitly describe < If required, perform a reboot manually after the update command completes >.

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Important
The update process does not reboot any nodes in the Overcloud automatically. If required, perform a reboot manually after the update command completes. 
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We are saying that ** zero downtime is doable **. But we are also saying that ** perform a reboot after the update command complete **.

Those kind of ambiguous description could make the customers confused, especially the customers who do want to avoid any downtime.

[1] https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/8/html/upgrading_red_hat_openstack_platform/chap-upgrading_the_environment#sect-Major-Upgrading_the_Overcloud-Compute

[2] https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/8/html/upgrading_red_hat_openstack_platform/chap-upgrading_the_environment

[3] https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux_openstack_platform/7/html/director_installation_and_usage/sect-updating_the_overcloud#sect-Updating_the_Overcloud_Packages