Add an option in Unity Cinder driver to customize the removing of empty host. The option is named `remove_empty_host`. Its default value is False. When it is set to True, the host will be removed from Unity after the last LUN is detached from it. Change-Id: I2d9fad2c977a61f5b26a6449a8e509911eff28e0 Closes-bug: #1768711 (cherry picked from commitf9a9aa5a25) (cherry picked from commit24bd0c4b64)
Release notes
The release notes for a patch should be included in the patch. The intended audience for release notes include deployers, administrators and end-users.
A release note is required if the patch has upgrade or API impact. It is also required if the patch adds a feature or fixes a long-standing or security bug.
Please see https://docs.openstack.org/cinder/latest/contributor/releasenotes.html for more details.